Defer implementation of MsgGenerator to prevent strange behaviour

[DiamondJoseph]

Previously it has been observed in blueapi that defining the same type alias in different modules has stopped being the same object, and then later stopped even being equal to each other. As checking that the return type of a function is MsgGenerator is used by blueapi to determine which plans to expose, this has prevented plans and stubs from being visible. As of bluesky 1.13, bluesky now defines its own implementation of MsgGenerator, which also meets the requirements of @rtuck99 of having a return type.

Prevents re-occurence of these issues and similar:
DiamondLightSource/blueapi#533
DiamondLightSource/blueapi#643

Instructions to reviewer on how to test:

1. Run type checking and ensure that functions that return a MsgGenerator are correctly typed
2. Confirm that

from dodal.common import MsgGenerator as m1
from bluesky.utils import MsgGenerator as m2

assert m1 is m2
assert m1 == m2

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}

[DiamondJoseph]

https://github.com/bluesky/bluesky/blob/b6828c53a68252caeefc3712ea50c49e507d8db2/src/bluesky/utils/__init__.py#L98

Here is the current implementation of MsgGenerator in bluesky.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.02%. Comparing base (e2b2705) to head (166fec9).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #832      +/-   ##
==========================================
- Coverage   95.02%   95.02%   -0.01%     
==========================================
  Files         117      117              
  Lines        4767     4764       -3     
==========================================
- Hits         4530     4527       -3     
  Misses        237      237              

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[callumforrester]

Unless you have a good reason to avoid it I would prefer this change were just a big find and replace where all imports within dodal are replaced with from bluesky.utils import MsgGenerator.

[DiamondJoseph]

Unless you have a good reason to avoid it I would prefer this change were just a big find and replace where all imports within dodal are replaced with from bluesky.utils import MsgGenerator.

Done

And PRs opened to allow eventual removal of dodal pass-through in other libraries too
DiamondLightSource/mx-bluesky#564
DiamondLightSource/blueapi#645

i22 etc. to follow