chore: key validator followups

[horsefacts]

Motivation

Followups from #354

Change Summary

• Validate that key length is exactly 32 bytes
• Add encodeMetadata view to SignedKeyRequestValidator. This exposes the SignedKeyRequest struct in the contract ABI for clients like Viem and can be called directly to encode metadata.
• Use the _registerValidator helper to explicitly set up validators in all tests, rather than rely on implicit setUp
• Comment cleanup

Merge Checklist

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• [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] All commits have been signed

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 making changes to the KeyRegistry, Bundler, and SignedKeyRequestValidator contracts.

Detailed summary

• Added virtual modifier to the setUp() function in BundlerTestSuite.sol
• Updated import statements in Bundler.gas.t.sol
• Added helper functions in SignedKeyRequestValidator.sol
• Modified the _signAdd() function in BundlerTestSuite.sol
• Updated the _signMetadata() function in SignedKeyRequestValidator.sol
• Made changes to the testFuzzAdd() function in KeyRegistry.integration.t.sol
• Made changes to the testFuzzAddRevertsShortKey() function in KeyRegistry.integration.t.sol
• Made changes to the testFuzzAddRevertsLongKey() function in KeyRegistry.integration.t.sol
• Updated the metadata parameter in the testFuzzAdd() function in KeyRegistry.integration.t.sol
• Updated the metadataType parameter in the testFuzzBulkAddSignerForMigration() function in KeyRegistry.t.sol
• Updated the metadataType parameter in the testFuzzBulkRemoveSignerForMigration() function in KeyRegistry.t.sol
• Updated the signerPk parameter to requesterPk in the testFuzzValidate() function in SignedKeyRequestValidator.t.sol

The following files were skipped due to too many changes: test/validators/SignedKeyRequestValidator/SignedKeyRequestValidator.t.sol

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[github-actions[bot]]

Coverage after merging horsefacts/key-validator-followups into main will be

98.94%

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
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%