v1.4.0 — Packet helpers, improved HMAC, dep updates & expanded docs

What's New

Features

• Add build_request_packet and decode_response_packet helper functions

Fixes

• Derive a separate mac_key from enc_key for response HMAC (improves key separation)
• Remove stale replay block referencing dropped mac field
• Replace rand_core 0.10 dep with 0.6; migrate rand 0.8 → 0.10 API

Documentation

• Expand module and function-level docs across the crate
• Move all imports to file tops for consistency
• Link to alterion-encrypt-js counterpart

CI

• Add CodeQL scanning on dev and main branches

Dependencies

• Update alterion-ecdh to stable 1.0
• Bump all deps to latest; fix hmac 0.13 KeyInit import