refactor: refactor climate.py (#614)

* feat: add thermostat as climate entity

* feat: add bath-heater as climate entity

* refactor: climate entity

* fix: thermostat on/off

* fix: get the current fan mode

* perf: get fan level

* fix: fix climate hvac_mode

* fix: misuse of getting key or value from dict[int, any]

* style: add comments

* style: format the file based on google style

* fix: initialize _attr_hvac_modes

* feat: add heat and defog mode of ptc bath heater

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Co-authored-by: topsworld <[email protected]>