Python: [BREAKING] Redesign Python exception hierarchy (#4082)

* [BREAKING] Redesign Python exception hierarchy

Replace the flat ServiceException family with domain-scoped branches:
- AgentException (with InvalidAuth, InvalidRequest, InvalidResponse, ContentFilter)
- ChatClientException (same consistent suberrors)
- IntegrationException (same + InitializationError)
- WorkflowException (Runner, Convergence, Checkpoint, Validation, Action, Declarative)
- ContentError (AdditionItemMismatch)
- ToolException / ToolExecutionException (unchanged)
- MiddlewareException / MiddlewareTermination (unchanged)

Key changes:
- All Service* exceptions removed (ServiceException, ServiceInitializationError, etc.)
- AgentExecutionException split into AgentInvalidRequest/ResponseException
- AgentInvocationError removed, split into AgentInvalidRequest/ResponseException
- Workflow exceptions moved from _workflows/_exceptions.py into main exceptions.py
- _workflows/__init__.py emptied; main __init__.py imports directly from submodules
- Purview exceptions re-parented under IntegrationException hierarchy
- Init validation errors use built-in ValueError/TypeError instead of custom exceptions
- CODING_STANDARD.md updated with hierarchy design and rationale

Fixes microsoft/agent-framework#3410

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

* Clarify ToolException vs ToolExecutionException docstrings

ToolException: base class for all tool-related exceptions (preconditions,
connection/init failures).
ToolExecutionException: runtime call failures (tool call failed, reconnect
failed, MCP errors).

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

* Fix remaining stale imports from agent_framework._workflows

- azurefunctions: _context.py, _app.py, _serialization.py, test_func_utils.py
  used 'from agent_framework._workflows import X' which broke after
  emptying _workflows/__init__.py; changed to direct submodule imports
- azure-ai-search: test still referenced ServiceInitializationError;
  updated to ValueError to match production code

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

---------

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

python/packages/foundry_local/agent_framework_foundry_local/_foundry_local_client.py

@@ -14,7 +14,6 @@ from agent_framework import (
     FunctionInvocationLayer,
 )
 from agent_framework._settings import load_settings
-from agent_framework.exceptions import ServiceInitializationError
 from agent_framework.observability import ChatTelemetryLayer
 from agent_framework.openai._chat_client import RawOpenAIChatClient
 from foundry_local import FoundryLocalManager
@@ -236,7 +235,7 @@ class FoundryLocalClient(
                 response = await client.get_response("Hello", options={"my_custom_option": "value"})
 
         Raises:
-            ServiceInitializationError: If the specified model ID or alias is not found.
+            ValueError: If the specified model ID or alias is not found.
                 Sometimes a model might be available but if you have specified a device
                 type that is not supported by the model, it will not be found.
 
@@ -263,7 +262,7 @@ class FoundryLocalClient(
                     "not found in Foundry Local."
                 )
             )
-            raise ServiceInitializationError(message)
+            raise ValueError(message)
         if prepare_model:
             manager.download_model(alias_or_model_id=model_info.id, device=device)
             manager.load_model(alias_or_model_id=model_info.id, device=device)

python/packages/foundry_local/tests/test_foundry_local_client.py

@@ -5,7 +5,7 @@ from unittest.mock import MagicMock, patch
 import pytest
 from agent_framework import SupportsChatGetResponse
 from agent_framework._settings import load_settings
-from agent_framework.exceptions import ServiceInitializationError, SettingNotFoundError
+from agent_framework.exceptions import SettingNotFoundError
 
 from agent_framework_foundry_local import FoundryLocalClient
 from agent_framework_foundry_local._foundry_local_client import FoundryLocalSettings
@@ -103,7 +103,7 @@ def test_foundry_local_client_init_model_not_found(mock_foundry_local_manager: M
             "agent_framework_foundry_local._foundry_local_client.FoundryLocalManager",
             return_value=mock_foundry_local_manager,
         ),
-        pytest.raises(ServiceInitializationError, match="not found in Foundry Local"),
+        pytest.raises(ValueError, match="not found in Foundry Local"),
     ):
         FoundryLocalClient(model_id="unknown-model")
 
@@ -171,7 +171,7 @@ def test_foundry_local_client_init_model_not_found_with_device(mock_foundry_loca
             "agent_framework_foundry_local._foundry_local_client.FoundryLocalManager",
             return_value=mock_foundry_local_manager,
         ),
-        pytest.raises(ServiceInitializationError, match="unknown-model:GPU.*not found"),
+        pytest.raises(ValueError, match="unknown-model:GPU.*not found"),
     ):
         FoundryLocalClient(model_id="unknown-model", device=DeviceType.GPU)