Subclass the built-in `TimeoutError`

When `astroquery.exceptions.TimeoutError` is raised, the traceback is misleading because it looks like it's actually python's built-in `TimeoutError` that is being raised. An example is here: https://github.com/nasa-fornax/fornax-demo-notebooks/issues/437#issuecomment-3377958977. @bsipocz suggested in https://github.com/nasa-fornax/fornax-demo-notebooks/pull/592 that astroquery should subclass the built-in error so that try/excepts that catch the built-in would also catch `astroquery.exceptions.TimeoutError`.

Start at the definition of astroquery.exceptions.TimeoutError and compare it with Python's built-in TimeoutError. Use the linked Fornax example as the behavior reference, then verify that the traceback identifies the astroquery exception and that catching the built-in also catches it.

Written by the indexing model from the issue text.