Summary

use dill._dill.get_file_type to open file types from _pyio, as using _pyio.open directly causes error from call of IOBase.__del__. Enables removal of some cleanup in test_selected.py

Checklist

Documentation and Tests

• Added relevant tests that run with python tests/__main__.py, and pass.
• Added relevant documentation that builds in sphinx without error.
• Added new features that are documented with examples.
• Artifacts produced with the main branch work as expected under this PR.

Release Management

• Added "Fixes #NNN" in the PR body, referencing the issue (#NNN) it closes.
• Added a comment to issue #NNN, linking back to this PR.
• Added rationale for any breakage of backwards compatibility.
• Requested a review.