Add type stubs for core analysis modules

[heejaechang]

Summary

• bundle complete sidecar stubs for radon.visitors, radon.raw, radon.complexity, and radon.metrics
• add the PEP 561 marker and explicit package data for legacy Setuptools builds
• preserve the complete runtime surface of each touched module, including result records and runtime reexports
• leave production Python modules unchanged

This is intentionally a partial typing contribution. The Mando-decorated CLI, harvesters, contrib plugin, and bundled tests remain untyped rather than being weakened or padded for a score.

Type completeness

Installed-wheel, unfiltered pyright --verifytypes radon --outputjson (no --ignoreexternal):

• score: 16.89% -> 53.23%
• known exports: 64 -> 247
• ambiguous exports: 19 -> 8
• unknown exports: 296 -> 209
• public modules: 28 -> 28

The two touched exports that remain unknown are the faithfully exposed stdlib operator module reexports in radon.raw and radon.visitors; they are not authored Any escape hatches.

Validation

• exact touched-module names, signatures, defaults, members, records, inheritance, mutability, and reexports match runtime introspection
• Python 3.7 grammar and Pyright target checks pass
• installed-wheel scoped mypy.stubtest passes without allowlists or exclusions
• strict positive consumers pass in Pyright and mypy; negative consumers reject invalid records, inputs, constructors, visitor calls, and member access
• 404 repository tests pass; available tox environments pass on Python 3.9 (400 tests) and 3.12 (404 tests); coverage remains 82%
• docs build succeeds with the same four existing warnings
• Poetry and Setuptools 67.8 wheel/sdist builds each contain exactly the four .pyi files plus py.typed
• representative analysis, result, deepcopy, and pickle behavior is identical on Python 3.9, 3.12, 3.13, 3.14, and 3.15
• added typing artifacts contain no Any, casts, ignores, noqa, checker disables, or allowlists

Follow-up contract audit

• distinguish Halstead dispatch results as string operator names and AST operands
• model values stored in operands_seen as Hashable and descriptor ownership as type[HalsteadVisitor]
• retain get_name(object) because runtime only reads obj.__class__.__name__
• retain broad keyword typing for from_code/from_ast: ParamSpec can follow subclass constructors only by falsely adding positional arguments that the runtime factories reject
• keep exported VerifyTypes metrics unchanged while improving referenced types from 1990 known / 58 ambiguous / 83 unknown to 1991 known / 56 ambiguous / 83 unknown

Existing boundaries

Full-package stubtest still stops before checking because untouched CLI/tests contain the existing untyped Mando import, tomllib/tomli redefinition, and bundled-test annotation errors. Twine still reports the existing README raw directive error. Existing repository-wide flake8/pep8/pylint failures and the obsolete make format tool arguments are unchanged; the added stubs pass targeted isort and Black checks.