feat: add SHA-256 integrity verification for C++ and Python (fixes #4)

[misakaAron]

Implements integrity verification as described in #4.

Changes

C++ (AntiCheat.cpp)

• Added SHA-256 hash computation using Windows CNG (BCrypt API)
• Added checkSelfIntegritySha256() function that compares SHA-256 of the running executable against a build-time constant JAVELIN_EXPECTED_SHA256
• Retained existing CRC32 check; SHA-256 runs as a stronger additional layer when configured
• Added oHex() utility for hash comparison output
• Exit code