(mx-bluesky#289) Add units to exposure_time parameter name

[JamesDoingStuff]

Fixes mx-bluesky#289

Instructions to reviewer on how to test:

1. Search repo for exposure_time variable
2. Ensure there are no occurrences that aren't renamed to exposure_time_s

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}

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.69%. Comparing base (fcfe95f) to head (71a5686).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1102   +/-   ##
=======================================
  Coverage   97.69%   97.69%           
=======================================
  Files         161      161           
  Lines        6652     6652           
=======================================
  Hits         6499     6499           
  Misses        153      153           

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[olliesilvester]

Looks good, anyone other than mx-bluesky who use DetectorParams will need to update too, although it might just be MX who use it

[DiamondJoseph]

it might just be MX who use it

I believe this is the case