Save last target temperature in Shelly climate platform

[bieniu]

Breaking change

Proposed change

Currently, target temperature value 4 means HVACMode OFF. When the mode is changed to HEAT, the target temperature is not changed, so the mode returns to mode OFF.
The change introduces the variable _last_target_temp, (with defaults value 20), target temperature is stored in this variable. When the HEAT mode is activated, the target temperature is set from this variable.

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 PR fixes or closes issue: fixes Shelly TRV HVAC operation mode cannot be turned to "heating" #80037
• 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
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• Tests have been added to verify that the new code works.

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[home-assistant]

Hey there @balloob, @thecode, @chemelli74, mind taking a look at this pull request as it has been labeled with an integration (shelly) you are listed as a code owner for? Thanks!

[thecode]

Looks good!