[OPIK-8197] [BE] fix: unhang PythonEvaluatorServiceTest and bound every test with a timeout - #8108

3 731 tests   - 14   3 729 ✅  - 14   2m 0s ⏱️ +6s
  447 suites + 1       2 💤 ± 0 
  447 files   + 1       0 ❌ ± 0 

Results for commit b192512. ± Comparison against earlier commit c04d283.