Add support for zhimi.heater.za2

[PRO-2684]

This PR adds support to zhimi.heater.za2.
heater_miot_za2.py's code is modified from heater_miot.py. Compared to already supported mc2 model, za2 can monitor relative humidity, so I added relative_humidity function.
P.S. Comment is wrong at heater_miot.py, line 21. Should be # Physical Control Locked (siid=5).

[rytilahti]

Hi and thanks for the PR!

Instead of creating a separate class that would necessitate separate tests etc., please just extend the existing implementation as they are from the same manufacturer and they do not differ that much.

You can do that by basing your PR on top of #1302, and introducing _mappings that is a dict containing model-keyed mappings. The correct mapping will then be chosen automatically run-time :-)

For the extra relative_humidity, you can check if the value is there and mark it as Optional in the container to keep the API for both types of models:

    @property
    def relative_humidity(self) -> int:
        """Current relative humidity."""
        return self.data.get("relative_humidity")

[PRO-2684]

On za2, LedBrightness 0 means "On (Bright)", 1 means "On (Dim)", 2 means "Off". How should this conflict be solved?

[PRO-2684]

@rytilahti This should work now. But as I modified the class LedBrightness, users may encounter compatibility issues.

[rytilahti]

Just two more things and this is good to go!

Btw, you can run the linting tests also locally by executing pre-commit run -a or tox -e lint, this way you can fix them without waiting for me to approve the run on CI.

[PRO-2684]

I've run the tests and it shall be fine now.

[rytilahti]

Please fix the tests and update README.md, and then this is good to go! 🎉

[rytilahti]

Oh, looks like the tests are still failing. Btw, you can also run the tests locally by executing pytest or tox :-)

[PRO-2684]

The reason why the tests are not passed is that the dummy test cases are based on mc2, but I chose to fall back on the strictest restriction in times of unrecognized models, including dummy.

[codecov-commenter]

Codecov Report

Merging #1301 (03492a0) into master (17e713a) will decrease coverage by 0.04%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master    #1301      +/-   ##
==========================================
- Coverage   82.34%   82.30%   -0.05%     
==========================================
  Files         106      106              
  Lines       11404    11417      +13     
  Branches     1354     1357       +3     
==========================================
+ Hits         9391     9397       +6     
- Misses       1821     1825       +4     
- Partials      192      195       +3     

Impacted Files	Coverage Δ
miio/heater_miot.py	87.35% <66.66%> (-7.24%)	⬇️

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[rytilahti]

This is good to go, thanks @PRO-2684!