fix: Graceful exit in BasicCrawler.run

[janbuchar]

• closes Handle KeyboardInterrupt gracefully #212

Before this, we got a traceback when CTRL+C was pressed during a crawl. Now we get this:

... history ...
INFO:httpx:HTTP Request: GET https://crawlee.dev/docs/3.7/quick-start "HTTP/1.1 200 OK"
INFO:httpx:HTTP Request: GET https://crawlee.dev/docs/3.6/quick-start "HTTP/1.1 200 OK"
^CINFO:crawlee.basic_crawler.basic_crawler:Pausing... Press CTRL+C again to force exit.
INFO:crawlee.autoscaling.autoscaled_pool:Waiting for remaining tasks to finish
INFO:crawlee.basic_crawler.basic_crawler:The crawl was interrupted. To resume, do: CRAWLEE_PURGE_ON_START=0 python some_crawling_script.py

[vdusek]

LGTM, just tests do not pass

[janbuchar]

To be continued with #228