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/azurefunctions/agent_framework_azurefunctions/_app.py

@@ -272,7 +272,7 @@ class AgentFunctionApp(DFAppBase):
             Note: We use str type annotations instead of dict to work around
             Azure Functions worker type validation issues with dict[str, Any].
             """
-            from agent_framework._workflows import State
+            from agent_framework._workflows._state import State
 
             data = json.loads(inputData)
             message_data = data["message"]

python/packages/azurefunctions/agent_framework_azurefunctions/_context.py

@@ -19,7 +19,7 @@ from agent_framework import (
     WorkflowEvent,
     WorkflowMessage,
 )
-from agent_framework._workflows import State
+from agent_framework._workflows._state import State
 
 
 class CapturingRunnerContext(RunnerContext):

python/packages/azurefunctions/agent_framework_azurefunctions/_serialization.py

@@ -23,7 +23,7 @@ import logging
 from dataclasses import is_dataclass
 from typing import Any
 
-from agent_framework._workflows import decode_checkpoint_value, encode_checkpoint_value
+from agent_framework._workflows._checkpoint_encoding import decode_checkpoint_value, encode_checkpoint_value
 
 logger = logging.getLogger(__name__)
 

python/packages/azurefunctions/tests/test_func_utils.py

@@ -182,7 +182,7 @@ class TestCapturingRunnerContext:
     @pytest.mark.asyncio
     async def test_create_checkpoint_raises_not_implemented(self, context: CapturingRunnerContext) -> None:
         """Test that checkpointing methods raise NotImplementedError."""
-        from agent_framework._workflows import State
+        from agent_framework._workflows._state import State
 
         with pytest.raises(NotImplementedError):
             await context.create_checkpoint("test_workflow", "abc123", State(), None, 1)