fix(restore): return from a failed restore without waiting for its cleanup

A failed or canceled native restore cleared its ongoing marker under a
fresh one-minute deadline, while the restore itself could still hold the
object lock that the cleanup waits for. The request then stalled for
about a minute (60 s in TestNativeRestoreWithoutOuterLock and
TestRestoreRecoversStrandedMarker).

Try the cleanup for 100 ms and leave the rest to the bounded background
retries, which already exist for the pools path and now also serve the
single-set path. Each retry still takes the object lock afresh and clears
only the marker of its own attempt. The CI restore race step drops from
about 260 s to 37 s.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Feng Ruohang <rh@vonng.com>

cmd/restore-native-isolation_test.go

@@ -455,7 +455,13 @@ func TestRestoreRecoversStrandedMarker(t *testing.T) {
 						t.Fatal(lerr)
 					}
 					ctx, cancel := context.WithTimeout(t.Context(), 100*time.Millisecond)
+					start := time.Now()
 					err = r.z.RestoreTransitionedObject(ctx, r.bucket, r.object, nativeRestoreOptions(r, oi.VersionID))
+					// The canceled caller must not wait for the minute-long
+					// background cleanup deadline before releasing its lock.
+					if elapsed := time.Since(start); elapsed > 5*time.Second {
+						t.Errorf("canceled restore blocked on marker cleanup for %s", elapsed)
+					}
 					cancel()
 					lk.Unlock(lkctx)
 				} else {