Pause the queue when it's empty and add a reason field when paused

[DominicOram]

Fixes #64

To test:

• Confirm new tests are good
• Confirm queue pauses when empty

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.63%. Comparing base (ab104c5) to head (ee0a3bf).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #69      +/-   ##
==========================================
+ Coverage   98.60%   98.63%   +0.03%     
==========================================
  Files          17       17              
  Lines         787      805      +18     
==========================================
+ Hits          776      794      +18     
  Misses         11       11              

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[jacob720]

Thanks, this looks good. Just a note, this makes it impossible to resume the queue if it's empty, which I think is fine but maybe should be documented somewhere