fix: Resolve lint and type-checking issues in A2A integration

- Remove unused imports (uuid, List, Part, TextPart)
- Fix type-checking errors for task_id and context_id validation
- Remove invalid AgentCard parameter (supported_content_types)
- Update test expectations for JSON output conversion
- Fix TaskInfo structure usage in cancel test
- Update server function call signatures in tests

All A2A tests now pass (34 passed, 2 skipped)

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

tests/a2a/test_exceptions.py

@@ -0,0 +1,56 @@
+"""Tests for A2A custom exceptions."""
+
+import pytest
+
+try:
+    from crewai.a2a.crew_agent_executor import (
+        A2AServerError,
+        TransportError,
+        ExecutionError
+    )
+    A2A_AVAILABLE = True
+except ImportError:
+    A2A_AVAILABLE = False
+
+
+@pytest.mark.skipif(not A2A_AVAILABLE, reason="A2A integration not available")
+class TestA2AExceptions:
+    """Test A2A custom exception classes."""
+    
+    def test_a2a_server_error_base(self):
+        """Test A2AServerError base exception."""
+        error = A2AServerError("Base error message")
+        
+        assert str(error) == "Base error message"
+        assert isinstance(error, Exception)
+    
+    def test_transport_error_inheritance(self):
+        """Test TransportError inherits from A2AServerError."""
+        error = TransportError("Transport configuration failed")
+        
+        assert str(error) == "Transport configuration failed"
+        assert isinstance(error, A2AServerError)
+        assert isinstance(error, Exception)
+    
+    def test_execution_error_inheritance(self):
+        """Test ExecutionError inherits from A2AServerError."""
+        error = ExecutionError("Crew execution failed")
+        
+        assert str(error) == "Crew execution failed"
+        assert isinstance(error, A2AServerError)
+        assert isinstance(error, Exception)
+    
+    def test_exception_raising(self):
+        """Test that exceptions can be raised and caught."""
+        with pytest.raises(TransportError) as exc_info:
+            raise TransportError("Test transport error")
+        
+        assert str(exc_info.value) == "Test transport error"
+        
+        with pytest.raises(ExecutionError) as exc_info:
+            raise ExecutionError("Test execution error")
+        
+        assert str(exc_info.value) == "Test execution error"
+        
+        with pytest.raises(A2AServerError):
+            raise TransportError("Should be caught as base class")