Automate onefile build in CI

[netanelcyber]

Problem

adpentest_onefile.py is currently regenerated by hand via a scratch script. It will drift from the package on any core change.

Proposal

• Move the assembly logic into scripts/build_onefile.py (checked in)
• Add a GitHub Actions job on push to main that:
  1. Runs the script
  2. Fails CI if adpentest_onefile.py differs from HEAD
  3. Runs python3 -m py_compile adpentest_onefile.py and a smoke import

Bonus

• Attach the built onefile as a release asset on tag pushes (v*).