perf(session): improve page management and speed up execution

Close pages immediately after tasks finish to reduce resource usage and
improve overall performance. Update corresponding test files to reflect
the new page lifecycle management.

tests/fetchers/async/test_dynamic_session.py

@@ -53,16 +53,18 @@ class TestAsyncDynamicSession:
         """Test page pool creation and reuse"""
         async with AsyncDynamicSession() as session:
             # The first request creates a page
-            _ = await session.fetch(urls["basic"])
-            assert session.page_pool.pages_count == 1
-
+            response = await session.fetch(urls["basic"])
+            assert response.status == 200
+            assert session.page_pool.pages_count == 0
+            
             # The second request should reuse the page
-            _ = await session.fetch(urls["html"])
-            assert session.page_pool.pages_count == 1
+            response = await session.fetch(urls["html"])
+            assert response.status == 200
+            assert session.page_pool.pages_count == 0
 
             # Check pool stats
             stats = session.get_pool_stats()
-            assert stats["total_pages"] == 1
+            assert stats["total_pages"] == 0
             assert stats["max_pages"] == 1
 
     async def test_dynamic_session_with_options(self, urls):