LETH / USD Spot Price Feed

[0xSpuddy]

Summary

Adds a LETH / USD feed for Veno finance that uses the ETH:LETH exchange rate multiplied by the ETH/USD price (medianized from exchanges).

Steps Taken to QA Changes

Tested locally and by submitting to Zksync Era Sepolia testnet: https://sepolia.explorer.zksync.io/tx/0x612a1726a22abc758a32a0ef3d573eb764e92654ca778aeb733afeb0edd7c592

Checklist

This pull request is:

• [x] A feature implementation

[0xSpuddy]

@akremstudy tried to improve the error handling and tests. lmk how it looks 🙏