feat(incrservice): add transactional offset resets (#26085)

This is the next prerequisite after #26027. It does not expose `ALTER TABLE ... AUTO_INCREMENT=N` yet.

The invariant in this PR is that an AUTO_INCREMENT offset reset and its allocator-cache transition belong to the same transaction:

- the resetting transaction sees its pending offset without publishing it to other transactions;
- statement or transaction rollback retires the private reset cache;
- commit publishes a cache for the allocation epoch actually used by the write;
- stale builders and old cache generations cannot become active after reset/reload/close;
- accepted allocator actions drain during close, while a canceled queued reset cannot mutate the store.

The shared service interface now carries `autoIncrEpoch` and `TxnOperator` through both production allocation callers. `memStore` and `sqlStore` gain monotonic `SetOffset` plus DDL-constrained `ForceSetOffset`; all implementations and mocks are updated atomically.

Out of scope for this PR:

- planner/compiler support for the user-facing ALTER syntax;
- COPY/CLONE allocator reconciliation;
- rolling-upgrade enablement for mixed-version TNs;
- end-to-end BVT for the final SQL behavior.

Diff size, separated for reviewability:

- production: `+1303 / -86`
- tests: `+1832 / -8`
- mocks: `+292 / -18`

Validation:

- `go test -race ./pkg/incrservice -count=1`
- `go test ./pkg/sql/colexec/preinsert ./pkg/sql/colexec/table_clone ./pkg/frontend/test ./pkg/vm/engine/test/testutil -count=1`
- `go test ./pkg/... -run '^$'`
- `git diff --check`
- exact-head `mo-pr-preflight-review`: PASS at `891781d3a927b80b54d38e381ebee0d749c1c589`

Approved by: @XuPeng-SH, @gouhongshen

Author: VioletQwQ-0

pkg/common/moerr/cause.go

@@ -104,10 +104,11 @@ var (
 	CauseAllocateTasks = NewInternalError(context.Background(), "allocateTask")
 	CauseTruncateTasks = NewInternalError(context.Background(), "truncateTasks")
 	//pkg/incrservice
-	CauseDoAllocate    = NewInternalError(context.Background(), "doAllocate")
-	CauseDoUpdate      = NewInternalError(context.Background(), "doUpdate")
-	CauseDestroyTables = NewInternalError(context.Background(), "destroyTables")
-	CauseAllocate      = NewInternalError(context.Background(), "allocate")
+	CauseDoAllocate       = NewInternalError(context.Background(), "doAllocate")
+	CauseDoUpdate         = NewInternalError(context.Background(), "doUpdate")
+	CauseDoForceSetOffset = NewInternalError(context.Background(), "doForceSetOffset")
+	CauseDestroyTables    = NewInternalError(context.Background(), "destroyTables")
+	CauseAllocate         = NewInternalError(context.Background(), "allocate")
 	//pkg/lockservice
 	CauseCleanCommitState          = NewInternalError(context.Background(), "cleanCommitState")
 	CauseValidateService           = NewInternalError(context.Background(), "validateService")

pkg/common/moerr/cause_test.go

@@ -98,6 +98,7 @@ var causeArray = []error{
 
 	CauseDoAllocate,
 	CauseDoUpdate,
+	CauseDoForceSetOffset,
 	CauseDestroyTables,
 	CauseAllocate,