feat(transfer): wire IORING_OP_RENAMEAT2 into remaining temp-file commit paths (#1924)

[oferchen]

Summary

• Wire fast_io::try_rename_via_io_uring() into the two remaining synchronous temp-file commit paths that still used plain std::fs::rename():
  • transfer_ops::response::process_file_response() - non-pipelined receiver path
  • receiver::transfer - synchronous receiver transfer loop
• On Linux 5.11+ with io_uring available, temp-file renames now submit IORING_OP_RENAMEAT instead of synchronous rename(2) in all transfer paths
• Falls back to std::fs::rename on non-Linux, older kernels, or when io_uring is disabled
• Completes the io_uring rename coverage started in feat: wire io_uring RENAMEAT2 and LINKAT into production paths #3981 (engine guard) and perf(transfer): wire io_uring RENAMEAT2/LINKAT into disk-commit path (#1924) #3992 (disk_commit pipeline)

Test plan

• cargo fmt --all -- --check passes
• cargo clippy --workspace --all-targets --all-features --no-deps -- -D warnings passes
• CI: nextest on Linux (stable) - exercises io_uring path on supported kernels
• CI: macOS (stable) - exercises fallback path (no io_uring)
• CI: Windows (stable) - exercises fallback path (no io_uring)
• CI: Linux musl (stable) - exercises io_uring or fallback depending on kernel
• Existing rename_with_io_uring_fallback and try_rename_via_io_uring unit tests in disk_commit/process.rs and fast_io/src/lib.rs continue to pass
• Interop tests validate end-to-end temp-file commit correctness on all platforms