Add vmxm gridscan plan

[olliesilvester]

Requires #1623 and DiamondLightSource/dodal#1925
Supersedes #924 and #1214

Note that these gridscans don't have ispyb integration. That is coming in a later PR

Link to dodal PR (if required): #XXX
(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. Do thing x
2. Confirm thing y happens

Checks for reviewer

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

[codecov]

Codecov Report

❌ Patch coverage is 92.68293% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.78%. Comparing base (a31185d) to head (4bce4b2).

Additional details and impacted files

@@                        Coverage Diff                        @@
##           364_make_nexus_callbacks_generic    #1636   +/-   ##
=================================================================
  Coverage                             92.78%   92.78%           
=================================================================
  Files                                   153      156    +3     
  Lines                                  8671     8757   +86     
=================================================================
+ Hits                                   8045     8125   +80     
- Misses                                  626      632    +6     

Components	Coverage Δ
i24 SSX	78.60% <ø> (ø)
hyperion	98.22% <ø> (ø)
other	97.99% <92.68%> (-0.12%)	⬇️

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