fix(client): cache subsequent clients

[nkaradzhov]

we dont need to recreate a client if
its config hasnt changed

fixes #2954

Description

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---

Checklist

• Does npm test pass with this change (including linting)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?

[nkaradzhov]

using the following test script we can see reasonable numbers

import { createClient, createClientPool, createCluster } from './packages/client'


const n = 200
const start1 = performance.now();
for (let i = 0; i < n; i++) {
  createClient();
}
console.log(`createClient(${n})`, performance.now() - start1);

const start2 = performance.now();
for (let i = 0; i < n; i++) {
  createClientPool();
}
console.log(`createClientPool(${n})`, performance.now() - start2);

const start3 = performance.now();
for (let i = 0; i < n; i++) {
 createCluster()
}
console.log(`createCluster(${n})`, performance.now() - start3);

[bobymicroby]

LGTM