Run tests weekly + Slack notification

[lola831]

Description

Adds a new scheduled workflow that runs our tests every Thursday at 9:15 AM (staggered 15 min past the hour to avoid peak runner load) and then posts a simple pass/fail message (with a link) into the Slack maintenance channel.

Issue Link

N/A

Checklist

• I have tested the changes locally via pytest and/or other means
• I have added or updated relevant documentation
• I have autoformatted the code with black and isort
• I have added test cases (if applicable)

Additional Notes

N/A

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.42%. Comparing base (c1003e9) to head (72589d7).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #347      +/-   ##
==========================================
- Coverage   91.45%   91.42%   -0.04%     
==========================================
  Files          54       54              
  Lines       13753    13746       -7     
==========================================
- Hits        12578    12567      -11     
- Misses       1175     1179       +4     

see 6 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[dfremont]

Looks good, thanks Lola!