Python: [BREAKING] Remove deprecated kwargs compatibility paths (#4858)

* [BREAKING] Remove deprecated kwargs compatibility paths

Remove the deprecated kwargs compatibility shims across core agents, clients, tools, middleware, and telemetry.

Keep workflow kwargs behavior intact in this branch and follow up separately in #4850.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Fix PR CI fallout for kwargs removal

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Address PR review feedback

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* updates

* Fix Azure AI CI fallout

Remove the stale _get_current_conversation_id override from the Azure AI client after the OpenAI base helper was deleted.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fixed new classes

* Fix Assistants deprecated import gating

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Fix integration replay regressions

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Switch multi-agent hosting samples to Azure chat completions

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Simplify Azure multi-agent sample config

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

python/packages/a2a/tests/test_a2a_agent.py

@@ -366,7 +366,7 @@ def test_get_uri_data_invalid_uri() -> None:
 def test_parse_contents_from_a2a_conversion(a2a_agent: A2AAgent) -> None:
     """Test A2A parts to contents conversion."""
 
-    agent = A2AAgent(name="Test Agent", client=MockA2AClient(), _http_client=None)
+    agent = A2AAgent(name="Test Agent", client=MockA2AClient(), http_client=None)
 
     # Create A2A parts
     parts = [Part(root=TextPart(text="First part")), Part(root=TextPart(text="Second part"))]
@@ -485,7 +485,7 @@ async def test_context_manager_no_cleanup_when_no_http_client() -> None:
 
     mock_a2a_client = MagicMock()
 
-    agent = A2AAgent(client=mock_a2a_client, _http_client=None)
+    agent = A2AAgent(client=mock_a2a_client, http_client=None)
 
     # This should not raise any errors
     async with agent:
@@ -495,7 +495,7 @@ async def test_context_manager_no_cleanup_when_no_http_client() -> None:
 def test_prepare_message_for_a2a_with_multiple_contents() -> None:
     """Test conversion of Message with multiple contents."""
 
-    agent = A2AAgent(client=MagicMock(), _http_client=None)
+    agent = A2AAgent(client=MagicMock(), http_client=None)
 
     # Create message with multiple content types
     message = Message(
@@ -523,7 +523,7 @@ def test_prepare_message_for_a2a_with_multiple_contents() -> None:
 def test_prepare_message_for_a2a_forwards_context_id() -> None:
     """Test conversion of Message preserves context_id without duplicating it in metadata."""
 
-    agent = A2AAgent(client=MagicMock(), _http_client=None)
+    agent = A2AAgent(client=MagicMock(), http_client=None)
 
     message = Message(
         role="user",
@@ -540,7 +540,7 @@ def test_prepare_message_for_a2a_forwards_context_id() -> None:
 def test_parse_contents_from_a2a_with_data_part() -> None:
     """Test conversion of A2A DataPart."""
 
-    agent = A2AAgent(client=MagicMock(), _http_client=None)
+    agent = A2AAgent(client=MagicMock(), http_client=None)
 
     # Create DataPart
     data_part = Part(root=DataPart(data={"key": "value", "number": 42}, metadata={"source": "test"}))
@@ -556,7 +556,7 @@ def test_parse_contents_from_a2a_with_data_part() -> None:
 
 def test_parse_contents_from_a2a_unknown_part_kind() -> None:
     """Test error handling for unknown A2A part kind."""
-    agent = A2AAgent(client=MagicMock(), _http_client=None)
+    agent = A2AAgent(client=MagicMock(), http_client=None)
 
     # Create a mock part with unknown kind
     mock_part = MagicMock()
@@ -569,7 +569,7 @@ def test_parse_contents_from_a2a_unknown_part_kind() -> None:
 def test_prepare_message_for_a2a_with_hosted_file() -> None:
     """Test conversion of Message with HostedFileContent to A2A message."""
 
-    agent = A2AAgent(client=MagicMock(), _http_client=None)
+    agent = A2AAgent(client=MagicMock(), http_client=None)
 
     # Create message with hosted file content
     message = Message(
@@ -595,7 +595,7 @@ def test_prepare_message_for_a2a_with_hosted_file() -> None:
 def test_parse_contents_from_a2a_with_hosted_file_uri() -> None:
     """Test conversion of A2A FilePart with hosted file URI back to UriContent."""
 
-    agent = A2AAgent(client=MagicMock(), _http_client=None)
+    agent = A2AAgent(client=MagicMock(), http_client=None)
 
     # Create FilePart with hosted file URI (simulating what A2A would send back)
     file_part = Part(