Configurable maximum concurrency in Risco local

[OnFreund]

Proposed change

Add a config flow option to the Risco integration to control the maximum number of concurrent requests to the panel.
Older panels have a hard time with high concurrency (and recent changes to HA startups also seem to require a lower value on newer panels), but setting it low will increase the amount of time required to get all zones and thus initialize the integration.
By making this configurable, advanced users can change this based on their panel and number of zones, and it will also serve as a useful troubleshooting step with other users.

Apart from #115118 this might also resolve #114049 and #114830.

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 Risco - Local - loading/retrieving zones and partitions fails -timing problems -Agility #115118
• This PR is related to issue:
• Link to documentation pull request: Document advanced Risco options home-assistant.io#32229

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.
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• 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

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To help with the load of incoming pull requests:

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[joostlek]

I think its a good idea to mention the existence of these options in the documentation