[Refactor] Simplify RPC client map key usage in getRpcClient function (#3805)
### TL;DR
Fixes an issue with RPC client reuse to improve performance.
### What changed?
The change replaces the use of `chainId` with `rpcUrl` as the key in the `rpcClientMap` to ensure the correct RPC client is reused.
### How to test?
Test by running existing unit tests and functional tests for RPC client related functionality. Ensure that performance metrics show improvement in RPC client reuse scenarios.
### Why make this change?
This change is motivated by the need to improve performance by ensuring the RPC client is correctly reused.
---