Treat session errors as regular request retries and drop `max_session_rotations`

SessionError has its own retry budget via max_session_rotations, on top of max_request_retries, which makes the effective retry count hard to reason about. JS v4 removed the separate budget: a session error retires the session and counts as a normal retry. Dropping use_session_pool (the pool is always on) belongs to the same cleanup.

JS implementation: apify/crawlee#3631, apify/crawlee#3478

✍️ Drafted by Claude Code