`async_wrapper` protocol yields `ModuleNotFoundError`

Trying to use the async_wrapper with url_to_fs to build an asynchronouos filesystem like:

fsspec.url_to_fs("async_wrapper://simplecache://https://www.foo.de")

It gives me a ModuleNotFoundError:

Traceback (most recent call last):
  File "/home/nils/projects/filesystem_spec/fsspec/registry.py", line 249, in get_filesystem_class
    register_implementation(protocol, _import_class(bit["class"]))
                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/nils/projects/filesystem_spec/fsspec/registry.py", line 284, in _import_class
    mod = importlib.import_module(mod)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/importlib/__init__.py", line 90, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<frozen importlib._bootstrap>", line 1387, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1360, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1324, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'fsspec.asyn_wrapper'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/home/nils/projects/filesystem_spec/fsspec/core.py", line 403, in url_to_fs
    chain = _un_chain(url, kwargs)
            ^^^^^^^^^^^^^^^^^^^^^^
  File "/home/nils/projects/filesystem_spec/fsspec/core.py", line 351, in _un_chain
    cls = get_filesystem_class(protocol)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/nils/projects/filesystem_spec/fsspec/registry.py", line 251, in get_filesystem_class
    raise ImportError(bit.get("err")) from e
ImportError: None

I tested with the up-to-date master branch (2025.3.2.post1+gaa1a301)

Start with fsspec/core.py at url_to_fs and _un_chain, then trace protocol loading through fsspec/registry.py at get_filesystem_class and _import_class. Reproduce the async_wrapper URL example and verify that it resolves the protocol without ModuleNotFoundError and supports the intended asynchronous filesystem chain.