feat(ecstore): io_uring runtime degradation latch + per-disk probe cache (rustfs/backlog#1101)
Follow-up to #1104. Add the runtime half of the io_uring degradation contract:
- Runtime latch: UringBackend gains an `active` flag (mirrors
DirectIoReadState::supported). A read that returns a restriction-class errno
(EPERM/EACCES/ENOSYS/EOPNOTSUPP) — io_uring became unusable on this disk —
trips the latch, and every further read goes straight to StdBackend with no
more per-read io_uring attempts. Data errors (EIO), missing files, and
parameter errors do NOT latch, since StdBackend would hit them too.
- Per-disk probe cache: a process-wide negative cache of disks whose probe
failed, so try_new skips re-probing (creating a ring + driver thread) on
reconnect.
Tests: the errno classifier (restriction-only) and a latched-off read that
still returns correct bytes via StdBackend; the #1104 differential test still
passes under real io_uring.
Co-authored-by: heihutu <[email protected]>
