feat: batch schema manager statements

run all schema modification queries in a single batch/transaction, to enable automatic rollbacks, and to stay within cloudflare's subrequest limits in free plan.

app/src/data/entities/EntityManager.ts

@@ -34,7 +34,6 @@ export class EntityManager<TBD extends object = DefaultDB> {
    private _entities: Entity[] = [];
    private _relations: EntityRelation[] = [];
    private _indices: EntityIndex[] = [];
-   private _schema?: SchemaManager;
    readonly emgr: EventManager<typeof EntityManager.Events>;
    static readonly Events = { ...MutatorEvents, ...RepositoryEvents };
 
@@ -249,11 +248,7 @@ export class EntityManager<TBD extends object = DefaultDB> {
    }
 
    schema() {
-      if (!this._schema) {
-         this._schema = new SchemaManager(this);
-      }
-
-      return this._schema;
+      return new SchemaManager(this);
    }
 
    // @todo: centralize and add tests