chore: add 3.1 deployment details

[horsefacts]

Motivation

Update README with 3.1 deployment details. Add Cyfrin audit doc.

Merge Checklist

Choose all relevant options below by adding an x now or at any time before submitting for review

• The PR title adheres to the conventional commits standard
• The PR has been tagged with change type label(s) (i.e. documentation, feature, bugfix, or chore)
• The PR's changes adhere to all the requirements in the contribution guidelines
• All commits have been signed

---

PR-Codex overview

This PR updates the contract names and adds a new contract.

Detailed summary

• Renamed Id Registry contract to track ownership of farcaster identities (fids)
• Renamed Storage Registry contract to allocate storage to fids and collect rent
• Renamed Key Registry contract to track associations between fids and key pairs
• Added new Id Gateway contract to issue farcaster identities
• Added new Key Gateway contract to add associations between fids and keys
• Updated contract addresses for deployment on OP Mainnet and Ethereum Mainnet
• Updated audit information for v3.1 contracts reviewed by Cyfrin

✨ Ask PR-Codex anything about this PR by commenting with /codex {your question}

[github-actions]

Coverage after merging horsefacts/v3.1-deployment into main will be

100.00%

Coverage Report

File	Stmts	Branches	Funcs	Lines	Uncovered Lines
src
Bundler.sol	100%	100%	100%	100%
FnameResolver.sol	100%	100%	100%	100%
IdGateway.sol	100%	100%	100%	100%
IdRegistry.sol	100%	100%	100%	100%
KeyGateway.sol	100%	100%	100%	100%
KeyRegistry.sol	98.56%	94.44%	100%	100%	153, 153
RecoveryProxy.sol	100%	100%	100%	100%
StorageRegistry.sol	100%	100%	100%	100%
src/abstract
EIP712.sol	100%	100%	100%	100%
Guardians.sol	100%	100%	100%	100%
Migration.sol	100%	100%	100%	100%
Nonces.sol	100%	100%	100%	100%
Signatures.sol	100%	100%	100%	100%
src/validators
SignedKeyRequestValidator.sol	100%	100%	100%	100%