Feat/rust and build perf

[alxxjohn]

PR summary:

This PR expands codeguard’s performance coverage across build-time and additional languages, and reconciles the supporting infrastructure
so the new checks dogfood cleanly.

What changed:

• Added first-class C++ performance support, including grammar/plumbing and initial high-precision rules.
• Added Go rebuild-cascade analysis using the in-repo package import graph, including hot-package and rebuild-amplifier findings.
• Added Rust build-time budget support via cargo --timings ingestion.
• Added broader build-regression support with baseline/compare plumbing for measured build commands.
• Updated docs, rule metadata, config types, defaults, validation, SDK exports, and fix templates for the new rules and budget kinds.
• Added tests covering the new C++, Go rebuild-cascade, cargo timings, and build-regression behavior.

Refactor and maintenance work included in the branch:

• Extracted shared helpers for language dispatch, reverse-dependency traversal, bounded subprocess execution, timing-budget measurement,
  and provider verdict decoding.

• Reduced duplicate logic between existing and new analyzers so future rule work lands in fewer places.

• Tuned repo-local dogfood thresholds in .codeguard/codeguard.yaml so codeguard’s own intentionally central packages do not self-flag under
  the new rebuild-cascade checks.

Benefits:

• Broader language/runtime coverage for real performance issues.
• New measured build-time capabilities instead of purely static heuristics.
• Lower maintenance overhead from shared helper extraction.
• Clean verification baseline: go test ./... and make codeguard-ci both pass on this branch.