feat: add tracing for compaction and manifest

[belveryin]

Summary:

• Instrumented compaction planning, scheduling, execution, and manifest-apply flows with consistent tracing spans and structured events.
• Added manifest CAS attempt/retry/failure events with stable, low-cardinality fields and table_id context.
• Replaced ad-hoc stderr logging with tracing events and added spans at key async boundaries.

Testing:

• cargo +nightly fmt --all -- --check
• cargo clippy --workspace -- -D warnings
• cargo build --verbose
• cargo test --verbose
• cargo llvm-cov --workspace --lcov --output-path target/coverage/lcov.info --fail-under-lines 80