[Zig] Expose HMAC in crypto module

[roninjin10]

Summary

Expose HMAC (Hash-based Message Authentication Code) in Zig crypto module.

Required Functions

• hmacSha256 - HMAC with SHA-256
• hmacSha512 - HMAC with SHA-512
• hmacKeccak256 - HMAC with Keccak-256
• Generic HMAC interface for different hash algorithms

Use Cases

• Key derivation (HKDF)
• Message authentication
• HD wallet derivation (uses HMAC-SHA512)
• API authentication

Current State

Not exposed in Zig crypto root module.

Note: Issue created by Claude AI assistant, not @roninjin10 or @fucory