feat(spiders/fetchers): Adding proxy rotation logic and change retry logic

- User passes a single proxy to the browser session, and it will keep using the same context. Pass a proxy manager that automatically refreshes the IP with each proxy, and you get speed but sacrifice some stealth.

- User imports the proxy rotator class and passes proxies to it and a rotation strategy (Round robin by default). Then pass the instance to the session class, which will create a context and a tab for each proxy returned by the rotator. This way, you sacrifice speed a bit, but you get maximum stealth since each context is created with the proxy that will be used.

- Normal requests use what you pass without issues, of course.

- All errors are retried now, and proxies are rotated on retries automatically.

scrapling/engines/toolbelt/__init__.py

@@ -1 +1,3 @@
+from .proxy_rotation import ProxyRotator, is_proxy_error, round_robin
 
+__all__ = ["ProxyRotator", "is_proxy_error", "round_robin"]