feat: Adds ADK EventActions to A2A response

Merge #3631

### Link to Issue or Description of Change

**1. Link to an existing issue (if applicable):**

- Closes: #3630

**Solution:**
Adds [Event.actions](https://github.com/google/adk-python/blob/a3aa07722a7de3e08807e86fd10f28938f0b267d/src/google/adk/events/event.py#L51) to A2A event metadata during ADK -> A2A event conversion (to allow A2A event consumers to access important info like state_delta, artifact delta, etc)

### Testing Plan

`pytest ./tests/unittests` passes

COPYBARA_INTEGRATE_REVIEW=#3631 from hoonji:main 31d3a49
PiperOrigin-RevId: 842274939

Author: hoonji

src/google/adk/a2a/converters/event_converter.py

@@ -140,6 +140,7 @@ def _get_context_metadata(
         ("custom_metadata", event.custom_metadata),
         ("usage_metadata", event.usage_metadata),
         ("error_code", event.error_code),
+        ("actions", event.actions),
     ]
 
     for field_name, field_value in optional_fields:

tests/unittests/a2a/converters/test_event_converter.py

@@ -66,8 +66,7 @@ def setup_method(self):
     self.mock_event.error_message = None
     self.mock_event.content = None
     self.mock_event.long_running_tool_ids = None
-    self.mock_event.actions = Mock(spec=EventActions)
-    self.mock_event.actions.artifact_delta = None
+    self.mock_event.actions = None
 
   def test_get_adk_event_metadata_key_success(self):
     """Test successful metadata key generation."""
@@ -144,6 +143,8 @@ def test_get_context_metadata_with_optional_fields(self):
     mock_metadata = Mock()
     mock_metadata.model_dump.return_value = {"test": "value"}
     self.mock_event.grounding_metadata = mock_metadata
+    self.mock_event.actions = Mock()
+    self.mock_event.actions.model_dump.return_value = {"test_actions": "value"}
 
     result = _get_context_metadata(
         self.mock_event, self.mock_invocation_context
@@ -152,7 +153,11 @@ def test_get_context_metadata_with_optional_fields(self):
     assert result is not None
     assert f"{ADK_METADATA_KEY_PREFIX}branch" in result
     assert f"{ADK_METADATA_KEY_PREFIX}grounding_metadata" in result
+    assert f"{ADK_METADATA_KEY_PREFIX}actions" in result
     assert result[f"{ADK_METADATA_KEY_PREFIX}branch"] == "test-branch"
+    assert result[f"{ADK_METADATA_KEY_PREFIX}actions"] == {
+        "test_actions": "value"
+    }
 
     # Check if error_code is in the result - it should be there since we set it
     if f"{ADK_METADATA_KEY_PREFIX}error_code" in result: