gh-109162: Refactor libregrtest.Regrtest

[vstinner]

• Add type hint types: TestName, StrPath, StrJSON.

• Add attributes to Regrtest:

  • cmdline_args
  • coverage
  • coverage_dir
  • fail_rerun
  • next_single_filename
  • print_slowest
  • tmp_dir
  • want_rerun
  • want_run_leaks

• Remove Regrtest.ns attribute.

• Rename Regrtest methods:

  • cleanup() => cleanup_temp_dir()
  • create_temp_dir() => make_temp_dir()
  • set_temp_dir() => select_temp_dir()

• Convert Regrtest methods to static methods:

  • cleanup_temp_dir()
  • display_header()
  • fix_umask()
  • get_rerun_match_tests()
  • list_tests()
  • make_temp_dir()
  • select_temp_dir()

• Remove display_sanitizers() method: move code into display_header().

• Rename 'test_cwd' variable to 'work_dir'.

• Issue: Refactor test.libregrtest #109162