refactor: add interfaces

[horsefacts]

Motivation

Minor, but this should make it easier to build on top of the various registries. Allows for it to be an easy reference for the interfaces and can be pulled into other projects to use, rather than needing to redefine it per project.

Change Summary

Simply adding interfaces. Main change is around where structs are located.

There are two options, not sure which one you prefer:

1. Structs within the interface
2. Structs in a *Structs.sol file and imported into the interface and implementation.

Merge Checklist

• 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

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PR-Codex overview

This PR focuses on adding interface contracts and updating existing contracts to implement these interfaces.

Detailed summary

• Added IStorageRegistry interface to StorageRegistry.sol
• Added IIdRegistry interface to IdRegistry.sol
• Added IKeyRegistry interface to KeyRegistry.sol
• Added IBundler interface to Bundler.sol
• Updated imports and function signatures to use the new interfaces

The following files were skipped due to too many changes: src/KeyRegistry.sol, test/KeyRegistry/KeyRegistry.t.sol, src/interfaces/IIdRegistry.sol, src/interfaces/IKeyRegistry.sol, src/interfaces/IStorageRegistry.sol, test/Bundler/Bundler.t.sol

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[sds]

Looks good to me, but will let @varunsrin make the final call on whether this gets merged.

[github-actions]

Coverage after merging kartik/interfaces 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%
RecoveryProxy.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%