pull request files collection could be more efficient

We might be able to squeeze a lot more performance from our api calls in PR files collection

Sonnet 4.6 has identified that we are constructing one graphql call per pull request:

https://github.com/chaoss/CollectOSS/blob/96adf3a4d68725db21622673ee6613693c0f5ace/collectoss/tasks/github/pull_requests/files_model/core.py#L52-L69

Some of these may return very few files.

Other places in the code already batch multiple queries into one graphQL call:

https://github.com/chaoss/CollectOSS/blob/96adf3a4d68725db21622673ee6613693c0f5ace/collectoss/tasks/frontend.py#L207-L212

We should do the same in pull request files to help make things faster (less waiting for network calls)

Start with collectoss/tasks/github/pull_requests/files_model/core.py at lines 52-69, then compare the batching approach in collectoss/tasks/frontend.py at lines 207-212. Confirm how pull request files are collected and identify the current per-pull-request GraphQL calls. Done means equivalent requests are batched to reduce network waits while preserving the collected files.

Written by the indexing model from the issue text.