Refactored to cpp20 and Qt6

.clang-format

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+# Copyright (C) 2016 Olivier Goffart <ogoffart@woboq.com>
+# SPDX-License-Identifier: BSD-3-Clause
+
+# This is the clang-format configuration style to be used by Qt,
+# based on the rules from https://wiki.qt.io/Qt_Coding_Style and
+# https://wiki.qt.io/Coding_Conventions
+
+---
+# Webkit style was loosely based on the Qt style
+BasedOnStyle: WebKit
+
+Standard: c++17
+
+# Column width is limited to 100 in accordance with Qt Coding Style.
+# https://wiki.qt.io/Qt_Coding_Style
+# Note that this may be changed at some point in the future.
+ColumnLimit: 100
+# How much weight do extra characters after the line length limit have.
+# PenaltyExcessCharacter: 4
+
+# Disable reflow of some specific comments
+# qdoc comments: indentation rules are different.
+# Translation comments and SPDX license identifiers are also excluded.
+# REUSE-IgnoreStart
+CommentPragmas: "^!|^:|^ SPDX-License-Identifier:"
+# REUSE-IgnoreEnd
+
+# We want a space between the type and the star for pointer types.
+PointerBindsToType: false
+
+# We generally use "template <" with space.
+SpaceAfterTemplateKeyword: true
+
+# We want to break before the operators, but not before a '='.
+BreakBeforeBinaryOperators: NonAssignment
+
+# Braces are usually attached, but not after functions or class declarations.
+BreakBeforeBraces: Custom
+BraceWrapping:
+    AfterClass: true
+    AfterControlStatement: false
+    AfterEnum: false
+    AfterFunction: true
+    AfterNamespace: false
+    AfterObjCDeclaration: false
+    AfterStruct: true
+    AfterUnion: false
+    BeforeCatch: false
+    BeforeElse: false
+    IndentBraces: false
+
+# When constructor initializers do not fit on one line, put them each on a new line.
+ConstructorInitializerAllOnOneLineOrOnePerLine: true
+# Indent initializers by 4 spaces
+ConstructorInitializerIndentWidth: 4
+
+# Indent width for line continuations.
+ContinuationIndentWidth: 8
+
+# No indentation for namespaces.
+NamespaceIndentation: None
+
+# Allow indentation for preprocessing directives (if/ifdef/endif). https://reviews.llvm.org/rL312125
+IndentPPDirectives: AfterHash
+# We only indent with 2 spaces for preprocessor directives
+PPIndentWidth: 2
+
+# Horizontally align arguments after an open bracket.
+# The coding style does not specify the following, but this is what gives
+# results closest to the existing code.
+AlignAfterOpenBracket: true
+AlwaysBreakTemplateDeclarations: true
+
+# Ideally we should also allow less short function in a single line, but
+# clang-format does not handle that.
+AllowShortFunctionsOnASingleLine: Inline
+
+# The coding style specifies some include order categories, but also tells to
+# separate categories with an empty line. It does not specify the order within
+# the categories. Since the SortInclude feature of clang-format does not
+# re-order includes separated by empty lines, the feature is not used.
+SortIncludes: false
+
+# macros for which the opening brace stays attached.
+ForEachMacros:   [ foreach, Q_FOREACH, BOOST_FOREACH, forever, Q_FOREVER, QBENCHMARK, QBENCHMARK_ONCE ]
+
+# Break constructor initializers before the colon and after the commas.
+BreakConstructorInitializers: BeforeColon
+
+# Add "// namespace <namespace>" comments on closing brace for a namespace
+# Ignored for namespaces that qualify as a short namespace,
+# see 'ShortNamespaceLines'
+FixNamespaceComments: true
+
+# Definition of how short a short namespace is, default 1
+ShortNamespaceLines: 1
+
+# When escaping newlines in a macro attach the '\' as far left as possible, e.g.
+##define a     \
+#   something; \
+#   other;     \
+#   thelastlineislong;
+AlignEscapedNewlines: Left
+
+# Avoids the addition of a space between an identifier and the
+# initializer list in list-initialization.
+SpaceBeforeCpp11BracedList: false
+
+# Do not reflow any comment
+ReflowComments: false
+
+---
+# Use the Google-based style for .proto files.
+Language: Proto
+BasedOnStyle: Google
+IndentWidth: 4
+ColumnLimit: 100

.github/workflows/ci-linux.yml

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+name: CI Linux
+
+on:
+  push:
+    branches: [ main, master ]
+  pull_request:
+
+jobs:
+  build-and-test:
+    # Ubuntu 24.04 ships Qt 6.4, which is the minimum the CMakeLists asks for.
+    runs-on: ubuntu-24.04
+    steps:
+      - uses: actions/checkout@v5
+        with:
+          fetch-depth: 0   # full history + tags, for the version from git describe
+
+      - name: Install dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y --no-install-recommends \
+            cmake ninja-build g++ \
+            qt6-base-dev \
+            libgtest-dev
+
+      - name: Configure
+        run: cmake -S . -B build -G Ninja -DCMAKE_BUILD_TYPE=Release
+
+      - name: Build
+        run: cmake --build build
+
+      - name: Test
+        run: ctest --test-dir build --output-on-failure

.github/workflows/ci-macos.yml

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+name: CI (macOS)
+
+on:
+  push:
+    branches: [ main, master ]
+  pull_request:
+
+jobs:
+  build-and-test:
+    # macos-14 is Apple Silicon; the clang_64 Qt kit is a universal build, so it works there.
+    runs-on: macos-14
+    steps:
+      - uses: actions/checkout@v5
+        with:
+          fetch-depth: 0   # full history + tags, for the version from git describe
+
+      - name: Install Qt
+        uses: jurplel/install-qt-action@v4
+        with:
+          version: 6.8.3
+          host: mac
+          arch: clang_64
+          cache: true
+
+      - name: Install build tools
+        run: brew install ninja googletest
+
+      - name: Configure
+        run: cmake -S . -B build -G Ninja -DCMAKE_BUILD_TYPE=Release
+
+      - name: Build
+        run: cmake --build build
+
+      - name: Test
+        run: ctest --test-dir build --output-on-failure

.github/workflows/ci-windows.yml

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+name: CI (Windows)
+
+on:
+  push:
+    branches: [ main, master ]
+  pull_request:
+
+jobs:
+  build-and-test:
+    runs-on: windows-2022
+    steps:
+      - uses: actions/checkout@v5
+        with:
+          fetch-depth: 0   # full history + tags, for the version from git describe
+
+      - name: Install Qt
+        uses: jurplel/install-qt-action@v4
+        with:
+          version: 6.8.3
+          host: windows
+          arch: win64_mingw
+          tools: tools_mingw1310
+          cache: true
+
+      # The runner's own gcc would not match the ABI of Qt's MinGW kit, so put the kit's first.
+      - name: Use Qt's MinGW toolchain
+        shell: bash
+        run: echo "$(cygpath -u "$QT_ROOT_DIR/../../Tools/mingw1310_64/bin")" >> "$GITHUB_PATH"
+
+      # No packaged GTest for Qt's MinGW kit, so build one with it.
+      - name: Install GTest
+        shell: bash
+        run: |
+          git clone --depth 1 --branch v1.15.2 https://github.com/google/googletest.git "$RUNNER_TEMP/googletest"
+          cmake -S "$RUNNER_TEMP/googletest" -B "$RUNNER_TEMP/googletest/build" -G Ninja -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX="$RUNNER_TEMP/gtest"
+          cmake --build "$RUNNER_TEMP/googletest/build"
+          cmake --install "$RUNNER_TEMP/googletest/build"
+          echo "GTest_ROOT=$RUNNER_TEMP/gtest" >> "$GITHUB_ENV"
+
+      - name: Configure
+        run: cmake -S . -B build -G Ninja -DCMAKE_BUILD_TYPE=Release
+
+      - name: Build
+        run: cmake --build build
+
+      - name: Test
+        run: ctest --test-dir build --output-on-failure