add explanatory docstrings to log.py

[Villtord]

Fixes #459

Instructions to reviewer on how to test:

1. Do thing x
2. Confirm thing y happens

Checks for reviewer

• Would the PR title make sense to a scientist on a set of release notes
• If a new device has been added does it follow the standards
• If changing the API for a pre-existing device, ensure that any beamlines using this device have updated their Bluesky plans accordingly
• Have the connection tests for the relevant beamline(s) been run via dodal connect ${BEAMLINE}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.03%. Comparing base (5951083) to head (d50aa29).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1854   +/-   ##
=======================================
  Coverage   99.03%   99.03%           
=======================================
  Files         305      305           
  Lines       11519    11519           
=======================================
  Hits        11408    11408           
  Misses        111      111           

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[DominicOram]

Great, thanks.