gh-151626: Fix tests that fail when PYTHONPYCACHEPREFIX is set

[zangjiucheng]

Summary

• Several tests in test_inspect, test_import, test_importlib.test_util,
  test_py_compile, and test_compileall assume the default __pycache__
  bytecode layout and fail when the suite is run with PYTHONPYCACHEPREFIX set.
• Fix: neutralize sys.pycache_prefix (and PYTHONPYCACHEPREFIX for
  subprocess-based tests) where that assumption is made so tests are environment-independent.
• The key pattern for subprocess tests: assert_python_ok() runs with -I
  (isolated mode), which ignores PYTHONPYCACHEPREFIX, so the expected cached
  path must be computed with sys.pycache_prefix=None to match.

• Issue: Some tests fail when __pycache__ prefix is set #151626

[vstinner]

test_inspect fails on Windows. Example:

FAIL: test_details_option_with_aliased_target (test.test_inspect.test_inspect.TestModuleCLI.test_details_option_with_aliased_target)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "D:\a\cpython\cpython\Lib\test\test_inspect\test_inspect.py", line 6676, in test_details_option_with_aliased_target
    self.assertEqual(output_lines, expected_lines)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: Lists differ: ['Tar[116 chars], 'Cached: None', 'Line: 98', ''] != ['Tar[116 chars], 'Cached: __pycache__\\frozencpython-316.pyc', 'Line: 98', '']

First differing element 3:
'Cached: None'
'Cached: __pycache__\\frozencpython-316.pyc'

  ['Target: ntpath:join (looked up as "os:path.join")',
   'Origin: frozen',
   'Source: D:\\a\\cpython\\cpython\\Lib\\ntpath.py',
-  'Cached: None',
+  'Cached: __pycache__\\frozencpython-316.pyc',
   'Line: 98',
   '']

[zangjiucheng]

I will resolve this today :)