Fix Rust raw-string attribute phantom imports

[Widthdom]

Summary

• Mask Rust attribute bodies before Rust type/use-position reference scanning so raw-string doc attributes cannot emit phantom use references.
• Add regression coverage for #[doc = r"use baz::qux;"] while keeping real use and call references.
• Add bilingual changelog fragment changelog.d/unreleased/1441.fixed.md.

Fixes #1441

Validation

• dotnet build CodeIndex.sln -c Release -p:UseSharedCompilation=false
• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj -c Release --filter "FullyQualifiedName~ReferenceExtractorTests.Extract_Rust" -p:UseSharedCompilation=false
• dotnet run --project tools/CodeIndex.Changelog -- check
• Adversarial review: No blocking/actionable issues found.

Notes

• A full dotnet test CodeIndex.sln -c Release -p:UseSharedCompilation=false run was attempted but stopped after several minutes of no test progress/output; focused Rust extractor tests and full ReferenceExtractorTests review pass completed successfully.
• AGENTS.md, CLAUDE.md, and AGENT_GUIDE.md were not modified.