[osipovartem]

Summary

• Observe writer completion while the demux channel remains open, so a failed writer cannot leave the sink waiting indefinitely for more input.
• Abort and join the demux and remaining writers before returning a setup or writer error. This provides the quiescence required by Iceberg cleanup of failed writes.
• Add a regression test with an open demux channel, one failing writer, and one waiting writer.

Verification

• Focused cargo +1.97.0 test -p datafusion-datasource-parquet --lib writer_error_waits_for_other_writers_to_stop: 1 passed locally after the Clippy fix.
• Targeted Rust 1.97 Clippy (-D warnings), Rust 1.94 cargo check -p datafusion (MSRV), cargo +1.97.0 fmt --all -- --check, and git diff --check passed locally.
• Independent read-only review of the final let-chain edit approved it without blocking findings.
• Rustice integration using the preceding writer-quiescence SHA 7955d2650 passed the 541-file, 4195-case strict SQLLogicTest corpus. The final 11874e4ba commit only collapses two behavior-equivalent conditions for Clippy; Rustice now pins that final SHA.

Performance and dependency

• Compared the preceding writer-quiescence SHA 7955d2650 with base 6770c7c34 using the same release-mode DataFusion harness; final 11874e4ba only changes behavior-equivalent let-chain syntax: 1,048,576 rows, one or 32 local Parquet files, five warmups and 20 samples per run, 15 alternating A/B pairs. Median paired change was +1.08% for one file (about 0.25 ms) and +1.58% for 32 files (about 1.6 ms). The shorter 131,072-row run was noisier (+4.32% and +0.1% over 20 pairs); the patched single-file run was faster in 9/20 pairs.
• This small measured local-write overhead is accepted to guarantee that failed writes stop before Iceberg removes uncommitted files. Coordination is per file/task completion, not per row; remote object-store performance was not measured.
• Independent read-only review approved the change without blocking findings. Remove uncommitted Iceberg data files after failed writes iceberg-rust#138 must only be consumed together with this writer-quiescence revision.

CI notes

• The MSRV job failed before compilation because cargo-msrv received HTTP 429 while fetching the Rust changelog; local Rust 1.94 compilation passed.
• The security audit reports 15 advisories in pre-existing Cargo.lock dependencies; this PR changes neither dependencies nor Cargo.lock.