[Copilot]

The build GitHub Actions job failed on lint-gated errors (E999, F821, F632) in committed Python files. This PR removes those blockers and adds focused regression tests so the workflow’s pytest step no longer fails due to empty test discovery.

• Lint-blocking syntax/name fixes

  • Corrected invalid f-string quoting in a2/exercise_1.py and a2/exercise_2.py.
  • Fixed undefined function reference in basic_math_recursion/task3/exercise_4.py by calling the existing function.
  • Replaced identity comparison with value comparison in h1/exercise_1.py (is → == for string literal).

• Targeted regression coverage

  • Added tests/test_build_fixes.py with focused assertions for:
    • status-code bucket aggregation (2xx, 4xx, 5xx) in both a2 exercises.
    • recursive Fibonacci path used by exercise_4.

• Representative change

  # before
  status = f"{request["status"][0]}xx"
  
  # after
  status = f"{request['status'][0]}xx"