fix: export pool getter from rds client (ali-sdk#102)

Author: fengmk2

lib/client.js

@@ -23,6 +23,10 @@ class RDSClient extends Operator {
     return await this.#pool.query(sql);
   }
 
+  get pool() {
+    return this.#pool;
+  }
+
   get stats() {
     return {
       acquiringConnections: this.#pool._acquiringConnections.length,

test/client.test.js

@@ -30,6 +30,10 @@ describe('test/client.test.js', () => {
   });
 
   describe('new RDSClient(options)', () => {
+    it('should access pool', async () => {
+      assert(db.pool.config.connectionConfig.database);
+    });
+
     it('should connect rds success', async () => {
       const rows = await db.query('show tables');
       // console.log(rows);