fix(logger): isolate failures between log sinks

[devmobasa]

Summary

• isolate write failures so one log sink cannot starve the other
• keep interrupted-write retries local to the affected sink
• bound retained formatting buffers and keep file records on one line

Validation

• cargo test logger::tests
• cargo test --no-default-features logger::tests
• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets --all-features -- -D warnings
• git diff --check