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/azure-ai-search/agent_framework_azure_ai_search/_context_provider.py

@@ -17,7 +17,6 @@ from agent_framework import AGENT_FRAMEWORK_USER_AGENT, Message
 from agent_framework._sessions import AgentSession, BaseContextProvider, SessionContext
 from agent_framework._settings import SecretString, load_settings
 from agent_framework.azure._entra_id_authentication import AzureCredentialTypes
-from agent_framework.exceptions import ServiceInitializationError
 from azure.core.credentials import AzureKeyCredential
 from azure.core.credentials_async import AsyncTokenCredential
 from azure.core.exceptions import ResourceNotFoundError
@@ -219,7 +218,7 @@ class AzureAISearchContextProvider(BaseContextProvider):
         )
 
         if mode == "agentic" and settings.get("index_name") and not model_deployment_name:
-            raise ServiceInitializationError(
+            raise ValueError(
                 "model_deployment_name is required for agentic mode when creating Knowledge Base from index."
             )
 
@@ -231,7 +230,7 @@ class AzureAISearchContextProvider(BaseContextProvider):
         elif settings.get("api_key"):
             resolved_credential = AzureKeyCredential(settings["api_key"].get_secret_value())  # type: ignore[union-attr]
         else:
-            raise ServiceInitializationError(
+            raise ValueError(
                 "Azure credential is required. Provide 'api_key' or 'credential' parameter "
                 "or set 'AZURE_SEARCH_API_KEY' environment variable."
             )

python/packages/azure-ai-search/tests/test_aisearch_context_provider.py

@@ -8,7 +8,7 @@ from unittest.mock import AsyncMock, Mock, patch
 import pytest
 from agent_framework import Message
 from agent_framework._sessions import AgentSession, SessionContext
-from agent_framework.exceptions import ServiceInitializationError, SettingNotFoundError
+from agent_framework.exceptions import SettingNotFoundError
 from azure.core.credentials import AzureKeyCredential
 
 from agent_framework_azure_ai_search._context_provider import AzureAISearchContextProvider
@@ -180,7 +180,7 @@ class TestInitCredentialResolution:
         assert provider.credential is akc
 
     def test_no_credential_raises(self) -> None:
-        with pytest.raises(ServiceInitializationError, match="Azure credential is required"):
+        with pytest.raises(ValueError, match="Azure credential is required"):
             AzureAISearchContextProvider(
                 endpoint="https://test.search.windows.net",
                 index_name="idx",
@@ -216,7 +216,7 @@ class TestInitAgenticValidation:
             )
 
     def test_missing_model_deployment_name_raises(self) -> None:
-        with pytest.raises(ServiceInitializationError, match="model_deployment_name"):
+        with pytest.raises(ValueError, match="model_deployment_name"):
             AzureAISearchContextProvider(
                 source_id="s",
                 endpoint="https://test.search.windows.net",