Redesign attribute callbacks

[GDYendell]

Summary

• AttrR.update and AttrR._on_update_callbacks -> AttrR._update_callback
  • Used to create an async task called periodically to update the attribute
• AttrR.set() -> AttrR.update()
• AttrW.process() -> AttrW.put(sync_setpoint: bool = False)
  • Transports should call without sync_setpoint
• AttrR._on_set_callbacks -> AttrR._on_update_callbacks
  • Called when the value in the attribute is updated. This is what transports register with to get the latest value.
  • In an AttrR or AttrRW without an IO, this is left unset so update does nothing.
• AttrW._process_callbacks -> AttrW._on_put_callback. This is called when a new value is put.
  • Calls send on the IO if it has one
  • In an AttrRW without an IO, the on_put_callback falls back to AttrRW.set so that internal driver parameters work as expected. This replaces the old SimpleHandler in a much simple way.
• AttrW._write_display_callbacks -> AttrW._sync_setpoint_callbacks
  • Called in put(sync_setpoint=True) to update the setpoint of the attribute being put, e.g. when a driver is manually putting to attributes based on user input such as a fan out
  • Called in AttrRW.update the first time to initialise the setpoints so that they aren't blank

Outstanding Questions

• Should transports ever call put with sync_setpoint=True? This will update the setpoints of all transports. I think it is useful to not do this so that it is clear when looking at the UI for a transport that the put was from somewhere else.
• Should fan out attributes call put with sync_setpoint=True? I think yes because it is effectively a user input and the UI should reflect that.
• Do the callback names make sense? Should on_put just be put, or something else?

[codecov]

Codecov Report

❌ Patch coverage is 93.57798% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.20%. Comparing base (019ae15) to head (1526ecd).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/fastcs/attributes.py	91.66%	6 Missing ⚠️
src/fastcs/launch.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #237      +/-   ##
==========================================
+ Coverage   90.18%   90.20%   +0.01%     
==========================================
  Files          45       45              
  Lines        2273     2276       +3     
==========================================
+ Hits         2050     2053       +3     
  Misses        223      223              

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