TST: extend check for leaked files
Use `ResourceWarning`s as indicators of leaked files. I left the `psutil`-based check for leaked files.

I enabled the check for leaked files for all io tests.

boto3 (#17058) is probably causing all of the unclosed ssl connections. This PR ignores ResourceWarnings that contain the string `'ssl'`. The fixture applied to all io tests further ignores all connections found by `psutils` for the same reason. Connections are checked for code that was previously covered by `check_file_leaks`.