fix(lockservice): fence stale binds by allocator epoch

[iamlinjunhong]

What type of PR is this?

• API-change
• BUG
• Improvement
• Documentation
• Feature
• Test and CI
• Code Refactoring

Which issue(s) this PR fixes:

issue #24896

What this PR does / why we need it:

fix(lockservice): fence stale binds by allocator epoch

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[aptend]

Review Result

Approved. I did not find any blocking issues in this PR.

What I Checked

• GetBind and KeepLockTableBind propagate the allocator epoch to CN.
• CN stale-bind purge follows the existing LockTable.Version semantics: cached binds with Version < observed allocator epoch are stale allocator state.
• main-branch bind-change handling was reviewed against the epoch purge path, including waiter cleanup and commit-side bind validation.
• The added tests cover get-bind refresh, keepalive failure/epoch refresh, concurrent observation, remote/proxy bind purge, and waiter cleanup.

Local Verification

git diff --check origin/main...HEAD
go test ./pkg/lockservice -run 'Test(CommitDetectsStaleLocalBindAfterAllocatorRestart|AllocatorVersionZeroKeepsLocalBinds|AllocatorObserverDoesNotPurgeSameEpochBindVersions|GetBindAllowsRegressedAllocatorVersionWithoutPurging|KeepaliveEpochPurgeKeepsGroupMovePop|AllocatorObserverPurgesRemoteAndProxyLockTables|AllocatorObserverConcurrentKeepaliveAndGetBind|AllocatorObserverCloseWaitersOnStaleLocalBind)$'
timeout 180s go test ./pkg/lockservice

Note: the full go test ./pkg/lockservice hit the 180s local timeout without output. The PR-specific test set passed locally, and CI is green.

[iamlinjunhong]

fixed the lockservice allocator-restart fencing issue across d4-24896, d3-24896, and m-24896.
Main fixes:
Added an allocator instance ID to lock table binds and allocator responses, so CNs can detect allocator replacement even when wall-clock-based versions regress or stay the same.
Updated CN-side stale bind detection to use allocator identity, not only monotonic allocator version.
Made allocator replacement purge go through normal bind-change fencing semantics, so active transactions get ErrLockTableBindChanged instead of lower-level closed/not-found errors.
Covered the combined keepalive unhappy path where OK=false and a newer/different allocator state arrive in the same response.
Ensured stale local, remote, and proxy lock tables are purged while current allocator-instance binds are preserved.
Added/updated regression tests for allocator ID changes, regressed allocator versions, keepalive cleanup, active txn fencing, remote/proxy stale bind cleanup, and concurrent observer paths.
For old branches, fixed remote-lock timeout handling to avoid recording phantom locks when the request likely never reached the remote owner.
Updated branch-specific tests whose old expectations conflicted with the new bind-change fencing behavior.