fix: recover persistent catalog WAL after restart

[weicao]

Root cause

DuckDB 1.5.5 replays COMMENT ON COLUMN as ReplayAlter -> SetColumnComment. When the table contains a generated column, replay rebinds the generated expression before the main database has been installed as DuckDB's default database, aborting startup with:

Calling DatabaseManager::GetDefaultDatabase with no default database set

The trigger matrix is specifically generated column + column comment; ordinary tables and generated tables without column comments reopen successfully.

Fix

• Initialize an in-memory DuckDB default catalog first.
• Register MyDuck scalar UDFs before persistent WAL replay.
• Attach and USE the configured persistent catalog after the default database exists.
• Initialize every later connection on the configured persistent catalog.
• Preserve Restart(true) with attach-level READ_ONLY; in-memory restart retains the prior DSN behavior.

This avoids a DuckDB dependency or Doltgres migration and is compatible with generated expressions that reference MyDuck UDFs.

Regression coverage

• ordinary/generated x with/without column comment matrix
• mysql_rand generated expression and BLOB-backed VECTOR storage shape
• file-position and GTID replication metadata
• schema, comment, generated data, vector bytes, and position snapshots before/after replay
• real subprocess exit without provider/DuckDB shutdown, followed by process reopen
• eight concurrent connections selecting the persistent default catalog
• two isolated providers with the same catalog name and no user tables in the in-memory bootstrap catalog
• read-only restart rejects writes and writable restart restores them

Verification

• go test -race -tags duckdb_arrow ./catalog -run '^(TestPersistentCatalogWALReplay|TestPersistentCatalogWALReplayAcrossProcess|TestPersistentCatalogProvidersAreIsolated|TestDatabaseProviderRestartClosesConnectionsBeforeReopen)$' -count=1
• GOFLAGS=-tags=duckdb_arrow go test ./catalog -count=1
• GOFLAGS=-tags=duckdb_arrow go test ./... -run '^$' -count=1
• GOFLAGS=-tags=duckdb_arrow go vet ./catalog
• focused generated/catalog/persistence engine tests pass

Candidate snapshot

• exact parent: 749b6164b105dafc08d627fa7ab522f4805c654b
• signed head: a56af4dccce0d40e2b84157a60026098dbfadbc8
• tree: 30453d90c23f446354ffa77a84dc9dd8b8e94646
• commit verification: GitHub verified, signed by GitHub
• files: catalog/provider.go, catalog/provider_restart_test.go, catalog/provider_wal_replay_test.go
• go.mod / go.sum: unchanged

Do not merge until independent review completes. The Doltgres v1.2.0 candidate remains separately blocked from merge or release until this fix is reviewed.

[leon-ape]

Approved exact signed head a56af4dccce0d40e2b84157a60026098dbfadbc8 only.

Local candidate validation passed: focused catalog restart/WAL replay (in-process and subprocess), provider isolation, and mysql_rand UDF registration stability; race run passed, focused tests passed, and diff-check passed. Scope is limited to catalog/provider.go, catalog/provider_restart_test.go, and catalog/provider_wal_replay_test.go; parent is exact 749b6164b105dafc08d627fa7ab522f4805c654b.

CI attempt 2 packages and Binlog Group 1 (including ServerRestart) passed. Go Query Engine failures match exact-parent run 32628342514/job 97167117220; Binlog Group 2 TestAutoRestartReplica matches exact-parent 32628342547/job 97167117056 (0 -> 1105, unsupported row-event flags 10). Attempt-1 CreateCatalog startup and AutoReconnect timing failures are non-reproducing/exact-base harness behavior per attached waiver. No product blocker found in this PR scope; do not merge or publish from this review.