Summary

• replace the string-lowering heuristic in metadata redaction with ASCII helpers that work on borrowed &str
• add dedicated case-insensitive contains/ends_with utilities to keep substring checks allocation-free
• extend metadata unit tests to verify case-insensitive redaction remains unchanged

Testing

• cargo +nightly fmt --
• cargo +1.90.0 clippy -- -D warnings
• cargo +1.90.0 build --all-targets
• cargo +1.90.0 test --all
• cargo +1.90.0 doc --no-deps
• cargo deny check
• cargo audit

https://chatgpt.com/codex/tasks/task_e_68d723bdfa9c832b9e8e08a6e4a65b70