Upgrade pyo3 0.26.0 -> 0.29.0

Needed to fix the build too.

1. Added rust/build.rs — calls
   add_extension_module_link_args() which emits -undefined
   dynamic_lookup on macOS. In pyo3 0.29, this is required
   because the crate's own build script must emit these linker
   flags (pyo3-ffi's build script no longer does it for
   downstream crates).
2. Added pyo3-build-config as a build-dependency
   in rust/Cargo.toml.
3. Added maturin to the dev dependency group in pyproject.toml
   so uv run maturin develop can find the maturin CLI.

Author: seddonym

justfile

@@ -23,7 +23,7 @@ compile-and-test:
 [group('testing')]
 [working-directory: 'rust']
 test-rust:
-    @cargo test --no-default-features
+    @PYO3_PYTHON="$(uv python find)" cargo test --no-default-features
 
 # Runs Python tests.
 [group('testing')]

pyproject.toml

@@ -41,6 +41,7 @@ Source-code = "https://github.com/python-grimp/grimp/"
 
 [dependency-groups]
 dev = [
+    "maturin>=1.0,<2.0",
     "import-linter>=2.5",
     "mypy>=1.18.2",
     "pre-commit>=4.3.0",