[florianaltendorfer]

Closes #4563.

Summary

• ScanContext gains in_string(offset), read off a second memoized mask that also blanks string bodies (mask_comments_and_strings(..., strings=True), which already understands Go raw strings). GoDialect.extract drops a route whose match starts in a string, so a test that writes another program's main.go in a backtick literal no longer reports that program's routes as the repo's providers.
• Only the match start is tested, so a real r.GET("/x", h) still matches even though its path is a string. Other dialects are unchanged, and test files are still scanned for providers.

Related Issues

Closes #4563

Test Plan

• Tests pass (pytest): new test_go_routes_in_a_raw_string_fixture_are_not_providers in tests/unit/workspace/test_contracts.py (fails on main), plus tests/unit/workspace and tests/unit/ingestion
• Lint passes (ruff check .)

Checklist

• My code follows the project's code style
• I have added tests for new functionality
• All existing tests still pass
• I have updated documentation if needed