fix: replace bare raise with return False in _restore_from_checkpoint

When _checkpoint_system_enabled is False, the method uses a bare
`raise` with no active exception, which causes RuntimeError at
runtime. The method's docstring says it returns False when restoration
is not possible, so return False is the correct behavior.

The caller in crawl() currently guards with `if
self._checkpoint_system_enabled`, but the method's own contract
should be self-consistent.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scrapling/spiders/engine.py

@@ -205,7 +205,7 @@ class CrawlerEngine:
         Returns True if successfully restored, False otherwise.
         """
         if not self._checkpoint_system_enabled:
-            raise
+            return False
 
         data = await self._checkpoint_manager.load()
         if data is None: