Relaying Withdrawals in L1 costs too much gas

[K-Ho]

Is your feature request related to a problem? Please describe.
https://etherscan.io/tx/0x383e3f21e198f04a0a6d17342bd6299d6056c92fafac7c732f5b1cb2dae7a33e
Relaying withdrawals currently costs ~500k gas

Describe the solution you'd like
Need to meter gas usage of relaying withdrawals and gas golf withdrawals down, ideally to <100k.
Potential fixes include:

• combining relayedMessages and successfulMessages
• Cheaper withdrawal costs by placing L2->L1 message hashes in a different part of the state trie

[K-Ho]

Useful: https://dashboard.tenderly.co/tx/main/0x383e3f21e198f04a0a6d17342bd6299d6056c92fafac7c732f5b1cb2dae7a33e/gas-usage

[K-Ho]

Closing for now since this is not a high priority.