Multipin snapshot fix

[rtuck99]

Fixes #1727

Link to dodal PR (if required): #N/A
(remember to update pyproject.toml with the dodal commit tag if you need it for tests to pass!)

Instructions to reviewer on how to test:

1. Tests pass
2. Multipin collections perform snapshot generation instead of capturing separate snapshots

Checks for reviewer

• Would the PR title make sense to a user on a set of release notes

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.02%. Comparing base (870e491) to head (1625ae7).

Additional details and impacted files

@@                           Coverage Diff                           @@
##           update_mx_bluesky_for_ophyd_async_0_17    #1753   +/-   ##
=======================================================================
  Coverage                                   93.01%   93.02%           
=======================================================================
  Files                                         164      164           
  Lines                                        8909     8913    +4     
=======================================================================
+ Hits                                         8287     8291    +4     
  Misses                                        622      622           

Components	Coverage Δ
i24 SSX	77.15% <ø> (ø)
hyperion	98.73% <100.00%> (+<0.01%)	⬆️
other	98.16% <ø> (ø)

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