[honbin]

Summary

• Add --field to read RFC3339 timestamps from a top-level JSON string field.
• Preserve matching JSONL records unchanged for downstream tools such as jq.
• Document the JSONL usage and how unparseable records are handled.

Verification

• cargo fmt --check — passed
• cargo clippy --workspace --all-targets -- -D warnings — passed
• cargo test -p window — passed
• Manually confirmed that an in-range JSONL record is output unchanged.
• cargo test --workspace is not fully passing: CLI tests for align and burst fail because their test helpers cannot find the corresponding executables.