feat(Signatures): support ERC1271 signatures

[horsefacts]

Motivation

Users should be able to perform signature-authenticated actions like fid registration/transfer and key registration from smart contract wallets.

Change Summary

Replace ECDSA with OpenZeppelin SignatureChecker in the Signatures helper.

Merge Checklist

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

• [x] The PR title adheres to the conventional commits standard
• [x] The PR has been tagged with change type label(s) (i.e. documentation, feature, bugfix, or chore)
• [x] The PR's changes adhere to all the requirements in the contribution guidelines
• [x] This PR does not require changes to the Farcaster protocol

Additional Context

If this is a relatively large or complex change, provide more details here that will help reviewers.

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PR-Codex overview

This PR focuses on replacing the usage of ECDSA library with SignatureChecker in multiple contracts.

Detailed summary

• Replaced ECDSA library import with SignatureChecker import in Signatures.sol
• Replaced "ECDSA: invalid signature" revert message with Signatures.InvalidSignature.selector in KeyRegistry.t.sol and IdRegistry.t.sol

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[github-actions[bot]]

Coverage after merging horsefacts/erc-1271-signatures into main will be

98.69%

Coverage Report

File	Stmts	Branches	Funcs	Lines	Uncovered Lines
src
Bundler.sol	100%	100%	100%	100%
FnameResolver.sol	100%	100%	100%	100%
IdRegistry.sol	100%	100%	100%	100%
KeyRegistry.sol	100%	100%	100%	100%
StorageRent.sol	100%	100%	100%	100%
src/lib
Signatures.sol	100%	100%	100%	100%
TransferHelper.sol	0%	0%	0%	0%	15, 15, 15, 25–26, 26, 26
TrustedCaller.sol	100%	100%	100%	100%