set core/chains/evm/forwarders `sendersCache` to LRU capped cache

[MitiaRD]

addressing a TODO comment in the codebase to replace the sendersCache variable from a map[common.Address][]common.Address to a LRU cache.

• Used the hashicorp library as the lru cache.
• Set arbitrary lru size to 20, not sure what an optimum value for lru size would be.
• Removed cacheMu sync.RWMutex set in the FwdMgr struct as the lru cache lib methods have internal lock mutex.

if the TODO comment is no longer required I can also remove it as a contribution 😄

[MitiaRD]

Hey @samsondav & @prashantkumar1982 👋 just wondering how I can get the pipelines to run, it seems they need to be approved for my first PR?

[github-actions[bot]]

This PR is stale because it has been open 60 days with no activity. Remove stale label or comment or this will be closed in 7 days.