build: make Rust quality gates exhaustive

[sandersonstabo]

Summary

• register every Rust target in the root Clippy and rustfmt aggregates
• add a deterministic read-only audit for BUILD/Cargo target registration and source ownership
• run the audit in native CI before Bazel setup
• normalize the four committed Rust 1.98 formatter offenders

Verification

• registration audit: 10 libraries, 9 binaries, 256 tests, 186 Cargo paths; zero findings
• negative fixture: removing one aggregate label exits 1 with exactly one finding
• cargo +1.98.0 metadata --locked --offline --no-deps
• bazel test --jobs=1 --nocache_test_results //:format_test
• bazel build --jobs=1 //:clippy (275 aspect applications; 2,219 actions)
• exact replay/blob/status/diff guards and Bazel shutdown

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Summary by cubic

Makes Rust quality gates exhaustive so every Rust target is actually covered by root Clippy and rustfmt; previously many targets were silently skipped.

Adds a deterministic read-only audit script that verifies BUILD/Cargo target registration and source ownership, and runs it in native CI before Bazel setup.

Migration

• The audit script runs via PowerShell in CI; no manual action needed locally.

Refactors

• Normalizes four committed Rust files to match rustfmt 1.98 formatting.

^{Written for commit e86c13e. Summary will update on new commits.}