test(lifecycle): regression test for expire/GET race (#3491) (#4706)

Adds a serial-lane ILM integration regression test that pins the
local-first ordering contract established by rustfs#3491, where
`expire_transitioned_object` deletes local metadata BEFORE any remote
tier cleanup so a concurrent GET can never observe live local metadata
pointing at an already-removed remote tier version (user-visible
`NoSuchVersion`).

`serial_tests::test_expire_transitioned_object_never_races_concurrent_get`
in `crates/scanner/tests/lifecycle_integration_test.rs`:

- Transitions an object to a mock warm tier, then runs a tight
  concurrent GET loop while calling `expire_transitioned_object`; every
  GET must return a full, correct body or a clean object/version-not-found
  -- never a tier-fetch failure.
- Deterministic ordering assertion (revert-proof): immediately after
  expiry the remote tier object is still present and the mock recorded
  zero remote `remove` calls, proving remote cleanup is deferred to
  free-version recovery. Reverting to remote-first ordering turns this
  assertion red.

Supporting changes:
- Re-export `expire_transitioned_object` from `api::bucket::lifecycle`.
- Record remote-tier mutating ops in the scanner test `MockWarmBackend`.
- Update tier-ilm-debugging.md to reference the new regression test.

Runs in the CI ILM Integration (serial) lane (ci.yml
test-ilm-integration-serial), picked up by the existing
binary(lifecycle_integration_test) filter.

Refs: rustfs/backlog#1148 (ilm-2), rustfs/backlog#1155

crates/ecstore/src/api/mod.rs

@@ -45,8 +45,8 @@ pub mod bucket {
             pub use crate::bucket::lifecycle::bucket_lifecycle_ops::{
                 ExpiryState, LifecycleOps, RestoreRequestOps, TransitionState, TransitionedObject, apply_expiry_rule,
                 apply_transition_rule, enqueue_expiry_for_existing_objects, enqueue_transition_for_existing_objects,
-                enqueue_transition_immediate, get_global_expiry_state, get_global_transition_state, init_background_expiry,
-                post_restore_opts, run_stale_multipart_upload_cleanup_once, validate_transition_tier,
+                enqueue_transition_immediate, expire_transitioned_object, get_global_expiry_state, get_global_transition_state,
+                init_background_expiry, post_restore_opts, run_stale_multipart_upload_cleanup_once, validate_transition_tier,
             };
         }