TST: Adding pytest to Project

[zdomke]

Adding empty tests and include some fixtures in conftest. Also added pytest configuation to pyproject.toml

Added some preliminary tests for:

1. Checking default values on startup
2. Checking that itemdelegates are added to the necessary columns in the tables used
3. Check initial row values for axis model and curves model
4. Testing the IOTimeParser is parsing out times correctly

Include some minor changes to files to account for using the tests:

• trace/main.py
  • Check if PyDMApplication.main_window exists before using it (does not exist in testing)
  • Check if logging_lbl is deleted before attempting to set its text (is deleted when testing is done)
• trace/mixins/file_io.py
  • Change import from datetime import datetime, timedelta --> import datetime (pytest patch for datetime.now() requires this change)
  • Change all subsequent calls for datetime --> datetime.datetime
  • Change all subsequent calls for timedelta --> datetime.timedelta

[zdomke]

Converting bits of code to Python 3.9 (instead of Python 3.10) since that is the version we are building and testing.