fix: scale and correct Rust coverage mapping

[cjorge-graphops]

Problems

1. Rust test-coverage import resolution rebuilt RustProductionFileIndex for every use specification. On a 648-production-file / 52-test-file workspace, coverage ran for more than 30 minutes at roughly 53,000 newfstatat calls per second.
2. Literal include!("path.rs") ownership was absent from the Rust dependency graph and direct-test mapping. Textually included implementation files were reported as zero-importer, untested modules even though they compile inside a directly tested owner.

Fix

• Cache the immutable production-file index by resolved project root and sorted production scope.
• Resolve literal Rust source include! edges in the dependency graph.
• Expand direct-test ownership recursively through literal includes, matching Rust compilation semantics.
• Add focused cache, graph, and recursive coverage regressions.

Verification

• Focused Rust/coverage tests: 25 passed.
• Full suite before the include change: 5,659 passed, 151 skipped; 5 unrelated baseline failures in Bash unused-import and review-prompt tests.
• Reproduction workspace: coverage completed in about 30 seconds instead of exceeding 30 minutes. Orphaned Rust files fell from 197 to 1, coverage findings fell from 306 to 158, and the full scan completed successfully.