docs: Add simple devices and plans for use in tutorials

[abbiemery]

With the removal of dodal as a dependency, we need to provide some simple devices and plans in order to follow through the tutorials. These are getting cleaned up in #1564.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.94%. Comparing base (f6eebe6) to head (223e8ce).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1577   +/-   ##
=======================================
  Coverage   95.93%   95.94%           
=======================================
  Files          44       44           
  Lines        3269     3277    +8     
=======================================
+ Hits         3136     3144    +8     
  Misses        133      133           

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[abbiemery]

This is just a direct copy of the wrapped count in dodal. I don't know if it is worth while paring this down to something more simple, or to add a move plan or something.

[tpoliaw]

I don't think we should have a direct copy - paring it down to the basic would make it clearer, eg the validation checks are not useful for tutorial purposes.

[abbiemery]

Is there a better place for this to live?

[tpoliaw]

utils would make the most sense if there's a way of getting it working without import order issues