refactor(schemas): remove NormalizedResponse backward-compat __init__; use canonical API

tests/test_ai_client_tool_loop.py

@@ -18,6 +18,7 @@ from unittest.mock import MagicMock, patch
 import pytest
 from src.result_types import Result
 from src.openai_compatible import NormalizedResponse, OpenAICompatibleRequest
+from src.openai_schemas import UsageStats
 from src.ai_client import run_with_tool_loop
 from src.vendor_capabilities import VendorCapabilities
 
@@ -28,8 +29,7 @@ def caps() -> VendorCapabilities:
 def _make_normalized_response(text: str = "ok", tool_calls: list[dict[str, Any]] | None = None) -> Result[NormalizedResponse]:
  return Result(data=NormalizedResponse(
   text=text, tool_calls=tool_calls or [],
-  usage_input_tokens=10, usage_output_tokens=5,
-  usage_cache_read_tokens=0, usage_cache_creation_tokens=0,
+  usage=UsageStats(input_tokens=10, output_tokens=5, cache_read_tokens=0, cache_creation_tokens=0),
   raw_response=None,
  ))