bpo-44554: refactor pdb targets (and internal tweaks) (GH-26992)

- Refactor module/script handling to share an interface (check method).
- Import functools and adjust tests for the new line number for find_function.
- Use cached_property for details.
- Add blurb.

Automerge-Triggered-By: GH:jaraco

Lib/test/test_pyclbr.py

@@ -222,7 +222,11 @@ class PyclbrTest(TestCase):
         cm('pickle', ignore=('partial', 'PickleBuffer'))
         cm('aifc', ignore=('_aifc_params',))  # set with = in module
         cm('sre_parse', ignore=('dump', 'groups', 'pos')) # from sre_constants import *; property
-        cm('pdb')
+        cm(
+            'pdb',
+            # pyclbr does not handle elegantly `typing` or properties
+            ignore=('Union', 'ModuleTarget', 'ScriptTarget'),
+        )
         cm('pydoc', ignore=('input', 'output',)) # properties
 
         # Tests for modules inside packages