Deal with cover assumed state

[balloob]

Description:

When a cover has an assumed state, we will always report the state as "50%" open. That way both commands can always be issued.

I've reached out to Google to ask if they can add support for commandOnlyOnOff to the OpenClose trait, like they have for the OnOff trait.

Related issue (if applicable): fixes #22672

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.

If the code does not interact with devices:

• Tests have been added to verify that the new code works.

[codecov]

Codecov Report

Merging #22673 into dev will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##              dev   #22673      +/-   ##
==========================================
+ Coverage   93.83%   93.83%   +<.01%     
==========================================
  Files         449      449              
  Lines       36551    36536      -15     
==========================================
- Hits        34296    34283      -13     
+ Misses       2255     2253       -2

Impacted Files	Coverage Δ
homeassistant/components/google_assistant/trait.py	96.28% <100%> (+0.48%)	⬆️
homeassistant/components/deconz/config_flow.py	97.72% <0%> (-0.24%)	⬇️
homeassistant/helpers/config_validation.py	95.46% <0%> (-0.03%)	⬇️
homeassistant/components/heos/config_flow.py	100% <0%> (ø)	⬆️
homeassistant/components/deconz/const.py	100% <0%> (ø)	⬆️

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