Cast top_path to Path in walk_modules function.

[simonjharris]

In some cases, the top_path variable is being set with a /./ in the path. It means that the string manipulation fails to extract the correct module name, and can lead to errors like the one below.

This PR casts the top_path to aPosixPath to match the base_path type. This strips out the additional /./ and means that the module name can be successfully extracted.

E.g.
top_path = "/var/task/./alembic_utils"

  File "/var/task/./alembic_utils/replaceable_entity.py", line 314, in compare_registered_entities
    if entity.__class__ not in registry.allowed_entity_types:
  File "/var/task/./alembic_utils/replaceable_entity.py", line 216, in allowed_entity_types
    return set(collect_subclasses(alembic_utils, ReplaceableEntity))
  File "/var/task/./alembic_utils/experimental/_collect_instances.py", line 78, in collect_subclasses
    for module_ in walk_modules(module):
  File "/var/task/./alembic_utils/experimental/_collect_instances.py", line 47, in walk_modules
    module = importlib.import_module(module_import_path)
  File "/var/lang/lib/python3.9/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1030, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1007, in _find_and_load
  File "<frozen importlib._bootstrap>", line 972, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 228, in _call_with_frames_removed
  File "<frozen importlib._bootstrap>", line 1030, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1007, in _find_and_load
  File "<frozen importlib._bootstrap>", line 984, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'embic_utils

[olirice]

Why is this PosixPath instead of Path?

won't that block windows support?

[simonjharris]

I'm not sure. I don't have a Windows machine to test it on. But from my debugging, base_path is already a PosixPath--or do you think that is platform-dependent?

[simonjharris]

Looks like you're right @olirice. Updated to use Path.