gh-108388: Split test_multiprocessing_spawn (#108396)

Split test_multiprocessing_fork, test_multiprocessing_forkserver and
test_multiprocessing_spawn into test packages. Each package is made
of 4 sub-tests: processes, threads, manager and misc. It allows
running more tests in parallel and so reduce the total test duration.

Lib/test/test_multiprocessing_forkserver/__init__.py

@@ -0,0 +1,13 @@
+import os.path
+import sys
+import unittest
+from test import support
+
+if support.PGO:
+    raise unittest.SkipTest("test is not helpful for PGO")
+
+if sys.platform == "win32":
+    raise unittest.SkipTest("forkserver is not available on Windows")
+
+def load_tests(*args):
+    return support.load_package_tests(os.path.dirname(__file__), *args)

Lib/test/test_multiprocessing_forkserver/test_manager.py

@@ -0,0 +1,7 @@
+import unittest
+from test._test_multiprocessing import install_tests_in_module_dict
+
+install_tests_in_module_dict(globals(), 'forkserver', only_type="manager")
+
+if __name__ == '__main__':
+    unittest.main()

Lib/test/test_multiprocessing_forkserver/test_misc.py

@@ -0,0 +1,7 @@
+import unittest
+from test._test_multiprocessing import install_tests_in_module_dict
+
+install_tests_in_module_dict(globals(), 'forkserver', exclude_types=True)
+
+if __name__ == '__main__':
+    unittest.main()

Lib/test/test_multiprocessing_forkserver/test_processes.py

@@ -0,0 +1,7 @@
+import unittest
+from test._test_multiprocessing import install_tests_in_module_dict
+
+install_tests_in_module_dict(globals(), 'forkserver', only_type="processes")
+
+if __name__ == '__main__':
+    unittest.main()

Lib/test/test_multiprocessing_forkserver/test_threads.py

@@ -0,0 +1,7 @@
+import unittest
+from test._test_multiprocessing import install_tests_in_module_dict
+
+install_tests_in_module_dict(globals(), 'forkserver', only_type="threads")
+
+if __name__ == '__main__':
+    unittest.main()