Add units to dwell time

[DominicOram]

Fixes #940

Link to dodal PR (if required): DiamondLightSource/dodal#213

To test:

1. Confirm tests pass

[codecov]

Codecov Report

Merging #941 (c587a5e) into main (ed29f84) will not change coverage.
Report is 10 commits behind head on main.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     DiamondLightSource/hyperion#941   +/-   ##
=======================================
  Coverage   93.33%   93.33%           
=======================================
  Files          52       52           
  Lines        2506     2506           
=======================================
  Hits         2339     2339           
  Misses        167      167           

Files	Coverage Δ
...l_interaction/callbacks/grid_detection_callback.py	100.00% <ø> (ø)
...plan_specific/stepped_grid_scan_internal_params.py	65.55% <100.00%> (ø)

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[noemifrisina]

Looks okay, thanks!

Question: is there also a change in GDA to go along with this?

[DominicOram]

Good spot, yes we will need a GDA change too

[DominicOram]

Actually, that code in GDA will be removed soon anyway (DiamondLightSource/mx-bluesky#347) so we should just do that instead