Add support for fetching bindkey from Mi cloud

[bdraco]

Proposed change

For v4 and v5 devices, you can provide your Xiaomi Cloud account login credentials for the account to which the device is bound, and Home Assistant will import the appropriate bind key from your account.

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 #
• This PR is related to issue:
• Link to documentation pull request: Document Xiaomi Cloud method is now available to get bindkeys for v4/v5 devices home-assistant.io#35328

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.

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[home-assistant]

Hey there @Jc2k, @Ernst79, mind taking a look at this pull request as it has been labeled with an integration (xiaomi_ble) you are listed as a code owner for? Thanks!

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[Jc2k]

This looks great. I've got some test devices out of storage so I'll test it locally, but that shouldn't block things.

[bdraco]

thanks. I'll adjust as needed in a followup if testing shows any changes are needed.