Split trace compare analysis helpers

[yvette-carlisle]

Summary

• Split pure trace compare analysis helpers into trace_compare/analysis.rs.
• Kept trace_compare.rs focused on async entrypoint, DB fetch, replay orchestration, and trace assembly.
• Added focused tests for stage deltas, attribution, invalid snapshot fallback, and valid nil UUID snapshot fallback.

Validation

• cargo make fmt-rust
• cargo make check-rust
• cargo make fmt-rust-check
• git diff --check
• cargo make lint-vstyle
• cargo nextest run -p elf-eval --all-targets --all-features trace_compare::analysis (6 passed)
• cargo make lint-rust
• cargo make test-rust (385 passed, 92 skipped)
• cargo make check (385 passed, 92 skipped)

Review

• Scout selected trace compare analysis as the next focused modularization boundary.
• Skeptic passed after the nil UUID fallback coverage gap was resolved.