CV2-6730: N+1 Query (task_response)

[melsawy]

Description

Both GraphQL fields first_response and first_response_value executed a separate database query for each Task to return the response which cause N+1 query pattern.

Added a loader (FirstResponseLoader) that batches all requested task IDs into a single query and caches the results for the duration of the GraphQL request. Both fields use the same loader, allowing them to reuse the fetched Annotation without issuing additional queries.

References: CV2-6730

How to test?

Re-run unit tests

Checklist

• I have performed a self-review of my code and ensured that it is safe and runnable, that code coverage has not decreased, and that there are no new Code Climate issues. I have also followed Meedan's internal coding guidelines.