Wait for eiger to disarm before stopping it

[DominicOram]

Fixes #935

Instructions to reviewer on how to test:

1. Confirm new test passes

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 (a822a40) to head (72a8563).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #936   +/-   ##
=======================================
  Coverage   97.51%   97.51%           
=======================================
  Files         152      152           
  Lines        6347     6354    +7     
=======================================
+ Hits         6189     6196    +7     
  Misses        158      158           

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[rtuck99]

Perhaps this fixes the issue, but I'm unclear on what exactly we should do in stop(), looking at bluesky run_engine.py it seems stop() is invoked in a variety of scenarios, including at the end of a plan, during a suspend and when pause() is invoked. The impression I get is that being stopped is at least somewhat resumable.

[DominicOram]

Sure but I think it's outside of the scope of this issue, I've made #994.