Speed up tests

[DominicOram]

Fixes #998

Instructions to reviewer on how to test:

1. Run the unit tests with pytest tests/
2. Confirm they are faster here than on main
3. Confirm tests are still sensible

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 97.51%. Comparing base (5fe0464) to head (ceedbae).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1000   +/-   ##
=======================================
  Coverage   97.51%   97.51%           
=======================================
  Files         152      152           
  Lines        6351     6351           
=======================================
  Hits         6193     6193           
  Misses        158      158           

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[Relm-Arrowny]

Looks good to me, sorry waiting time never crossed my mine back then.