Support macOS WeChat 4.1.x Config.Cipher key extraction

[beijinguang]

Summary

• Add macOS 4.1.x Config.Cipher memory discovery and XOR blob decoding.
• Validate extracted candidates against database-page HMAC, supporting HMAC-SHA1 for newer WeChat and retaining HMAC-SHA512 compatibility.
• Include the rebuilt macOS arm64 helper binary and emit salt metadata for reliable validation.

Verification

• macOS C scanner builds with -Wall -Wextra -Werror.
• Offline synthetic Config.Cipher candidate regression check passes.
• Offline HMAC-SHA1 and HMAC-SHA512 regression checks pass.
• git diff --check passes.

The HMAC compatibility portion overlaps the currently open #22; it can be coordinated with that PR during review.