Add ZHA ZCL thermostat entities

[Caius-Bonus]

Proposed change

Add ZCL Thermostat UI entity: Keypad Lockout
Add ZCL Thermostat entities: min_heat_setpoint_limit, max_heat_setpoint_limit, pi_heating_demand, setpoint_change_source

Most of these are mandatory ZCL attributes, so it is reasonable to expect devices to implement them.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

This is closely related to the Danfoss PR: #86907

This is however not specific to Danfoss, which makes it logical to make a separate PR. This will also make it easier to review.

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• I have followed the perfect PR recommendations
• The code has been formatted using Ruff (ruff format homeassistant tests)
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

If the code communicates with devices, web services, or third-party tools:

• The manifest file has all fields filled out correctly.
  Updated and included derived files by running: python3 -m script.hassfest.
• New or updated dependencies have been added to requirements_all.txt.
  Updated by running python3 -m script.gen_requirements_all.
• For the updated dependencies - a link to the changelog, or at minimum a diff between library versions is added to the PR description.
• Untested files have been added to .coveragerc.

To help with the load of incoming pull requests:

• I have reviewed two other open pull requests in this repository.

[Caius-Bonus]

Ready for merge again.

[Caius-Bonus]

Ready for merge

[TheJulianJES]

Seems to look pretty good.

Maybe also change the capitalization(s) in some of the added docstrings (and add a dot at the end, although this doesn't seem to be a requirement anymore).

[Caius-Bonus]

Thanks, just fixed up the docstrings

[TheJulianJES]

Seems to look good now!

[Caius-Bonus]

Ready for merge again.

[TheJulianJES]

Still good! Thanks again.