Add optional integrity verification

[NguyenTienDat-GTR]

Closes #4

Summary:

• Add optional CRC32 self-integrity enforcement for the Windows C++ executable via JAVELIN_EXPECTED_CRC32.
• Add a Python guard that checks the running script SHA-256 against JAVELIN_EXPECTED_SHA256.
• Return guarded exit codes for integrity, debugger, and suspicious-process failures.
• Document how to compute and set expected integrity values.

Verification:

• uv run python -m unittest -v
  • Ran 7 tests: OK

Note:

• C++ compile verification was not run locally because no cl, g++, or clang++ compiler was available in this environment.