Refactor libclang parser and Reuse in unit rule

[melodyoncode]

• refactor(cpp/libclang): extract reusable parser action

  • Move the C++ parser action setup into shared Starlark plumbing so it can be reused by both cpp_parser and other Bazel rules.
  • Switch parser outputs from an output directory to explicit class FlatBuffer and optional debug JSON files, and update the Rust CLI and docs to use those paths.

• test(cpp/libclang): centralize parser integration case wiring

  • Add a shared integration test macro that wires the parser, expected output filegroup, debug JSON provider, and Rust comparison test for each case.
  • Update all parser integration BUILD files to use the macro and make the test framework consume the explicit debug JSON output path.

• feat(rules_score): generate implementation class FBS in unit rule

  • Wire the libclang C++ parser action into the unit rule for implementation targets that provide parser inputs.
  • Collect generated class diagram FBS files in DefaultInfo, and add the parser toolchain attrs/aspects required by the reused action.