Stop purging the request queue on repeated run() calls #2305

A repeated run() on the same crawler purges the default request queue (run(purge_request_queue=True) in _basic_crawler.py), so the second run re-crawls everything locally. JS v4 stopped doing that: a repeated run continues where the previous one left off.

Proposed solution

• Remove the purge_request_queue argument of run() and the implicit purge. purge() stays on the request manager for anyone who wants to start over.
• When a crawl processes nothing because its request manager holds only handled requests, log a warning that says why. This also catches a second crawler on a shared queue and a queue that a previous process worked through. Starting against handled requests stays silent, since that is what resuming looks like.
• Document the alternatives for re-crawling: an explicit purge(), or a fresh alias per run.

This will be a breaking change.

JS implementation: apify/crawlee#4056 (related apify/crawlee#3367)

✍️ Drafted by Claude Code