Fix manager_agent handling in Crew.copy() method

This commit addresses issue #2260 by:
1. Adding manager_agent to the exclude list in the Crew.copy() method
2. Implementing proper error handling for manager_agent copying
3. Adding comprehensive tests to verify the fix
4. Enhancing test data for better coverage
5. Improving docstrings for better code documentation

Co-Authored-By: Joe Moura <joao@crewai.com>

tests/test_data/test_kickoff_for_each.json

@@ -1 +1,8 @@
-{"foo": ["document1", "document2"]}
+{
+    "foo": ["document1", "document2"],
+    "empty": [],
+    "special_chars": ["doc#1", "doc@2"],
+    "nested": {
+        "documents": ["nested1", "nested2"]
+    }
+}