fix: dynamic import cjs module pg (#685)

Co-authored-by: Alex Yang <himself65@outlook.com>

packages/core/src/storage/vectorStore/PGVectorStore.ts

@@ -82,7 +82,9 @@ export class PGVectorStore implements VectorStore {
   private async getDb(): Promise<pg.Client> {
     if (!this.db) {
       try {
-        const { Client } = await import("pg");
+        const pg = await import("pg");
+        const { Client } = pg.default ? pg.default : pg;
+
         const { registerType } = await import("pgvector/pg");
         // Create DB connection
         // Read connection params from env - see comment block above