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/anthropic/agent_framework_anthropic/_chat_client.py

@@ -28,7 +28,6 @@ from agent_framework import (
 )
 from agent_framework._settings import SecretString, load_settings
 from agent_framework._types import _get_data_bytes_as_str  # type: ignore
-from agent_framework.exceptions import ServiceInitializationError
 from agent_framework.observability import ChatTelemetryLayer
 from anthropic import AsyncAnthropic
 from anthropic.types.beta import (
@@ -303,7 +302,7 @@ class AnthropicClient(
 
         if anthropic_client is None:
             if not anthropic_settings["api_key"]:
-                raise ServiceInitializationError(
+                raise ValueError(
                     "Anthropic API key is required. Set via 'api_key' parameter "
                     "or 'ANTHROPIC_API_KEY' environment variable."
                 )

python/packages/anthropic/tests/test_anthropic_client.py

@@ -14,7 +14,6 @@ from agent_framework import (
     tool,
 )
 from agent_framework._settings import load_settings
-from agent_framework.exceptions import ServiceInitializationError
 from anthropic.types.beta import (
     BetaMessage,
     BetaTextBlock,
@@ -128,7 +127,7 @@ def test_anthropic_client_init_missing_api_key() -> None:
     with patch("agent_framework_anthropic._chat_client.load_settings") as mock_load:
         mock_load.return_value = {"api_key": None, "chat_model_id": "claude-3-5-sonnet-20241022"}
 
-        with pytest.raises(ServiceInitializationError, match="Anthropic API key is required"):
+        with pytest.raises(ValueError, match="Anthropic API key is required"):
             AnthropicClient()