Log info on processed batch for topic-extract on arxiv

[FrancescoCasalegno]

Description

Currently, we are logging info while we extract topic info for all sources but arxvi.

The reason why arxiv is special is that we don't send requests to the server using the arxiv ids one by one, but in batches.

So this PR introduces batch-based logging info for arxiv topic extraction.

Checklist

• This PR refers to an issue from the issue tracker.
  (if it is not the case, please create an issue first).
• Unit tests added.
  (if needed)
• Documentation and whatsnew.rst updated.
  (if needed)
• setup.py and requirements.txt updated with new dependencies.
  (if needed)
• Type annotations added.
  (if a function is added or modified)
• All CI tests pass.

[jankrepl]

LGTM

[EmilieDel]

LGTM! Thank you!