added BaseIntrospector and reorganized connections

app/src/data/connection/DummyConnection.ts

@@ -1,7 +1,11 @@
-import { Connection } from "./Connection";
+import { Connection, type FieldSpec, type SchemaResponse } from "./Connection";
 
 export class DummyConnection extends Connection {
    constructor() {
       super(undefined as any);
    }
+
+   override getFieldSchema(spec: FieldSpec, strict?: boolean): SchemaResponse {
+      throw new Error("Method not implemented.");
+   }
 }