Ruff errors

[lochhh]

Ruff check is failing with the following errors:

• swc/aeon/io/api.py:174:13: PLC0415 import should be at the top-level of a file
• tests/io/test_api.py:57:5: PT031 pytest.warns() block should contain a single simple statement
• tests/io/test_api.py:57:23: PT030 pytest.warns(UserWarning) is too broad, set the match parameter or use a more specific warning