fix(taskprocessing): use the event for AppAPI to get list of AI providers

[oleksandr-nc]

Summary

Currently, external Task Processing providers (like those from AppAPI ExApps) might need to be loaded and registered on every request during AppAPI bootstrap, potentially impacting performance. This PR introduces an event-driven mechanism to allow the core Task Processing Manager to discover these providers on demand.

1. New Event: Introduced OCP\TaskProcessing\Events\GetTaskProcessingProvidersEvent. This event is dispatched by the Manager when it needs to build the list of available providers and task types.

2. A request-scoped static cache within dispatchGetProvidersEvent prevents redundant dispatching within the same request twice(fisrt time for Providers list and second time for custom TasksTypes list)

TODO

• PR with use of this event in AppAPI repository

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[marcelklehr]

Can we extend the tests for this?

[oleksandr-nc]

Can we extend the tests for this?

I think it might be more effective to place the integration tests in the AppAPI or ExApps repositories, where they can actually validate the Provider registration end-to-end. Mocking the tests here might not fully cover both parts of the system, and events system in the Nextcloud Server is already covered with tests.

[marcelklehr]

Thanks 💙

[kyteinsky]

🚀

[oleksandr-nc]

/backport to stable31