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/tests/test_shared.py

@@ -7,7 +7,7 @@ import pytest
 from agent_framework import (
     FunctionTool,
 )
-from agent_framework.exceptions import ServiceInvalidRequestError
+from agent_framework.exceptions import IntegrationInvalidRequestException
 from azure.ai.agents.models import CodeInterpreterToolDefinition
 from pydantic import BaseModel
 
@@ -387,7 +387,7 @@ def test_create_text_format_config_text() -> None:
 
 def test_create_text_format_config_invalid_raises() -> None:
     """Test invalid response_format raises error."""
-    with pytest.raises(ServiceInvalidRequestError):
+    with pytest.raises(IntegrationInvalidRequestException):
         create_text_format_config({"type": "invalid"})
 
 
@@ -400,7 +400,7 @@ def test_convert_response_format_with_format_key() -> None:
 
 def test_convert_response_format_json_schema_missing_schema_raises() -> None:
     """Test json_schema without schema raises error."""
-    with pytest.raises(ServiceInvalidRequestError, match="requires a schema"):
+    with pytest.raises(IntegrationInvalidRequestException, match="requires a schema"):
         _convert_response_format({"type": "json_schema", "json_schema": {}})