Have input_output tests create files to a temporary directory instead of to the main DESC directory

[dpanici]

Per title, currently the io tests create a writer and reader test file in the DESC directory, so when ran locally they create test files in the top level of the project directory. Really not a big issue and affects nothing but if a user runs the tests locally and finds new files in their home directory it might look a little strange.

Should be an easy enough fix to have the tests use a temporary directory using like the tmp_dir feature of pytest, but I was too lazy to make the fix so just putting this note here for now.

[ddudt]

This is low priority, we won't worry about it for now.