feat: add mappings and platform statistics to IdentityManagerV2

[malgus01]

Pull Request

Summary

This PR enhances the IdentityManagerV2 contract by introducing essential mappings and platform statistics for improved verification tracking and user management.

Changes

• Added platform statistics
  • Introduced VerificationStats public stats to maintain global verification metrics.
• Added mappings with full Natspec documentation
  • nullifierHashes: track used nullifier hashes.
  • userVerifications: map user addresses to their verification data.
  • usersByType: group verified users by UserType.
  • userPositions: track user indices in usersByType arrays for efficient removal.
  • verifiedUserPositions: track user indices in verifiedUsers array for efficient removal.
• Added verifiedUsers array for easy enumeration of all verified accounts.
• Formatting
  • Ran forge fmt for consistent code style.

Motivation

These changes introduce core data structures needed for:

• Efficient user verification tracking.
• Organized user management by type.
• Improved on-chain analytics via platform statistics.
• Easier user enumeration and removal operations.