Add the components to test the postgres database on github actions

[stephen-riggs]

This adds a postgres database to the github workflows, with an exposed port. The connection environment variable are then passed onto all tests.

The url and engine for the postgres database are in a new tests/__init__.py file for importing into test files. In tests/conftest.py is a common fixture that can be used to setup the database for all tests, and adds a sample murfey session to it.

As an example of this test setup, I have written tests for the register_grid_square function in the position analysis.

Also fixes a bug in the position analysis where file paths are secured into strings.

[codecov]

Codecov Report

Attention: Patch coverage is 40.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 27.30%. Comparing base (153719e) to head (1ca3091).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #465      +/-   ##
==========================================
+ Coverage   27.06%   27.30%   +0.24%     
==========================================
  Files          78       78              
  Lines       10293    10293              
  Branches     1361     1361              
==========================================
+ Hits         2786     2811      +25     
+ Misses       7419     7390      -29     
- Partials       88       92       +4     

[tieneupin]

Looks good. Thanks so much for figuring out how to implement database testing!