fix: 按完成时刻分批清理并限制读连接池

internal/store/migrate_test.go

@@ -36,7 +36,7 @@ func TestFailingMigrationReusesBackup(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	if len(first) != 1 || first[0].Name() != "pre-migrate-v2-to-v9999.db" {
+	if len(first) != 1 || first[0].Name() != "pre-migrate-v4-to-v9999.db" {
 		t.Fatalf("first backups=%v", dirNames(first))
 	}