feat(ecstore): runtime-probed io_uring read backend, gray-off by default (backlog#1104) (#4632)

feat(ecstore): add runtime-probed io_uring read backend, gray-off by default (rustfs/backlog#1104)

Wire the standalone rustfs-uring crate (https://github.com/rustfs/uring) into
LocalIoBackend as an opt-in read backend. When RUSTFS_IO_URING_READ_ENABLE is
set AND the per-disk io_uring probe succeeds, positioned reads go through the
cancel-safe UringDriver; otherwise — default, or on a restricted host, or on
any per-read driver error — reads fall back to StdBackend byte-for-byte, so the
default build is unchanged.

- Cargo.toml: rustfs-uring as a Linux-only git dependency (pinned rev). The
  guard scripts/check_no_tokio_io_uring.sh allows an explicit io-uring
  integration; only the tokio "io-uring" runtime feature is banned.
- UringBackend mirrors StdBackend::pread_bytes's resolution/access/bounds
  preamble and only swaps the raw byte read; the other three trait methods
  delegate to the inner StdBackend.
- Backend selection at LocalDisk construction via build_local_io_backend.
- Differential test uring_backend_reads_match_std: with the flag set, every
  positioned read returns byte-identical data (driver-served when io_uring is
  available, StdBackend fallback otherwise).

Verified: cargo check -p rustfs-ecstore on Linux; the differential test passes
under real io_uring (seccomp=unconfined). The runtime errno degradation latch,
per-disk probe cache, and productionization are tracked in
rustfs/backlog#1101/#1102.

Co-authored-by: heihutu <heihutu@gmail.com>

.github/workflows/audit.yml

@@ -112,4 +112,9 @@ jobs:
         with:
           fail-on-severity: moderate
           allow-ghsas: GHSA-2f9f-gq7v-9h6m
+          # rustfs-uring is a first-party Apache-2.0 crate pulled as a git
+          # dependency (backlog#1104); its license cannot be read from the git
+          # source, so allow it explicitly to avoid a spurious unknown-license
+          # warning on every Cargo.lock change.
+          allow-dependencies-licenses: pkg:cargo/rustfs-uring
           comment-summary-in-pr: always