chore: extract shared EIP712 base contract

[horsefacts]

Motivation

As we've worked on consuming these contracts from Warpcast, we've added a few EIP-712 helper views. These are useful for clients debugging their own EIP-712 signatures. This PR cleans up our EIP712-related functionality and adds consistent helper views everywhere by extracting a shared abstract base contract.

Change Summary

Refactor all contracts using EIP-712 signatures to use our own EIP712 base contract, which inherits OZ EIP712 and exposes hashTypedDataV4 and domainSeparatorV4. Expose typehashes as public constants. Remove most test harness wrappers, which are no longer needed.

Merge Checklist

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• The PR title adheres to the conventional commits standard
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PR-Codex overview

Detailed summary

This PR focuses on making several changes and improvements to the codebase. The notable changes include:

• Adding a new assumption in KeyRegistry.integration.t.sol
• Importing and using IdRegistry in IdRegistry.gas.t.sol
• Changing the function name and adding a constant in SignedKeyRequestValidator.t.sol
• Changing the function name and adding a constant in KeyRegistry.t.sol
• Changing the function name and adding a constant in IdRegistry.owner.t.sol
• Adding a new contract and importing dependencies in EIP712.sol
• Changing the gas usage in several tests
• Changing the imports and contracts in BundlerTestSuite.sol
• Changing the function name and adding a constant in FnameResolver.t.sol
• Changing the function name and adding a constant in IdRegistry.t.sol
• Changing the imports and contracts in SignedKeyRequestValidatorTestSuite.sol
• Changing the imports and contracts in KeyRegistryTestSuite.sol
• Changing the imports and contracts in FnameResolverTestSuite.sol

The following files were skipped due to too many changes: test/FnameResolver/FnameResolverTestSuite.sol, src/KeyRegistry.sol, src/validators/SignedKeyRequestValidator.sol, src/FnameResolver.sol, test/IdRegistry/IdRegistryTestSuite.sol, test/Deploy/DeployL1.t.sol, test/Utils.sol, src/IdRegistry.sol

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[github-actions]

Coverage after merging horsefacts/shared-eip-712-contract into main will be

98.65%

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%
StorageRegistry.sol	100%	100%	100%	100%
src/lib
EIP712.sol	50%	100%	50%	50%	19
Signatures.sol	100%	100%	100%	100%
TransferHelper.sol	0%	0%	0%	0%	12, 17, 20, 20, 20
TrustedCaller.sol	100%	100%	100%	100%
src/validators
SignedKeyRequestValidator.sol	100%	100%	100%	100%