Add LED brightness for Xiaomi Miio ZA5 fan

[bieniu]

Breaking change

Proposed change

This PR adds LED brightness entity (number platform) for ZA5 fan.

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)
• 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 #
• This PR is related to issue: xiaomi_miio - Standing Fan 3 (ZHIMI.FAN.ZA5) LED switch missing #59789
• Link to documentation pull request: Add information about LED brightness entity for Xiaomi Miio ZA5 fan home-assistant.io#20398

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
• The code has been formatted using Black (black --fast 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.

The integration reached or maintains the following Integration Quality Scale:

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To help with the load of incoming pull requests:

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

[probot-home-assistant]

This pull request needs to be manually signed off by @home-assistant/core before it can get merged.
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[probot-home-assistant]

Hey there @rytilahti, @syssi, @starkillerOG, mind taking a look at this pull request as it has been labeled with an integration (xiaomi_miio) you are listed as a code owner for? Thanks!
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[MartinHjelmare]

Looks good!

Would be good to follow up separately and remove the similar OscillationAngleValues modifications.