Refactor/email auth simplification

[zkfriendly]

Description

This PR introduces a new simplified EmailAuthSigner contract that provides a signature-like authentication mechanism using emails. Unlike the existing EmailAuth contract which handles nullifiers internally, this new contract is designed to be used like a signature verification mechanism where the calling contract manages its own replay protection.

Key changes:

• Added new EmailAuthSigner.sol contract
• Created IEmailAuth.sol interface to standardize common functionality
• Moved EmailAuthMsg struct to the interface
• Updated existing contracts to implement the interface
• Added comprehensive tests for the new signer contract

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How Has This Been Tested?

Added new test files and cases:

• EmailAuthSigner.t.sol with comprehensive test coverage including:
  • Basic initialization and configuration
  • DKIM registry updates
  • Verifier updates
  • Email authentication
  • Error cases and invalid inputs
  • Upgrade functionality
  • Template ID validation

All existing tests have been updated to work with the interface changes and continue to pass.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[openzeppelin-code]

Refactor/email auth simplification

Generated at commit: 8b411892165dbe43efcc92240aa660c8b026650b

🚨 Report Summary

	Severity Level	Results
Contracts	Critical High Medium Low Note Total	0 1 0 6 28 35
Dependencies	Critical High Medium Low Note Total	0 0 0 0 0 0

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For more details view the full report in OpenZeppelin Code Inspector