feat(analysis): add Rust support to UnifiedParser (.rs) (#4506)

Register Rust in the UnifiedParser so it parses .rs files and emits the
standard metric set, backed by TreeSitterExcavationSite v0.12.0 (which adds
Rust code metrics).

- FileExtension: add RUST(".rs")
- AvailableCollectors + TreeSitterAdapter: map .rs -> Language.RUST
- bump TSE dependency v0.7.0 -> v0.12.0
- tests: RustCollectorTest (9 cases) and the parameterized golden
  (rustSample.rs / rustSample.cc.json), plus TreeSitterAdapter mapping lists
- docs: README + gh-pages supported-languages table and per-metric
  subsections, CHANGELOG

Co-authored-by: Christian Hühn <christian.huehn@maibornwolff.de>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>