Harden archive reads and corrupted block recovery

[LessUp]

Summary

• harden archive reader validation for footer/index offsets, block header stream extents, and read-count invariants
• fix corrupted-block recovery so placeholder reads are emitted consistently across sequential, parallel, pipeline, and original-order decompression
• add end-to-end regressions for malformed archives, paired-layout orchestration, and corrupted-block placeholder recovery

Test Plan

• cargo fmt --all -- --check
• cargo clippy --all-targets -- -D warnings
• cargo test --lib --tests
• cargo doc --no-deps
• npm run docs:build