fix(schemas): add legacy-kwarg backward compat to NormalizedResponse.__init__

12 tests fail with:
  TypeError: NormalizedResponse.__init__() got an unexpected keyword argument 'usage_input_tokens'

The @dataclass(frozen=True) auto-generated __init__ requires `usage: UsageStats`,
but 12 tests + 1 production site (src/ai_client.py:908) call it with the OLD
flat-kwarg API (usage_input_tokens=..., usage_output_tokens=..., etc.).

Change @dataclass(frozen=True) -> @dataclass(frozen=True, init=False) and add
a custom __init__ that accepts BOTH signatures:
- New: usage: UsageStats (used by current production code)
- Legacy: usage_input_tokens, usage_output_tokens, usage_cache_read_tokens,
  usage_cache_creation_tokens (used by tests + 1 ai_client site)

If usage is None and any legacy flat kwarg is non-None, build a UsageStats
from the legacy kwargs. Otherwise use the provided usage. All field
assignments use object.__setattr__ because frozen=True locks __setattr__.

Verification:
- Legacy kwargs work: NormalizedResponse(text="hi", tool_calls=(), usage_input_tokens=10, usage_output_tokens=5, raw_response=None) sets usage.input_tokens=10
- New kwargs work: NormalizedResponse(text="hi", tool_calls=(), usage=UsageStats(1, 2)) sets usage directly
- 12 affected tests now pass (was 12 failed, 3 passed; now 15 passed)

src/openai_schemas.py

@@ -72,13 +72,36 @@ class UsageStats:
  cache_creation_tokens: int = 0
 
 
-@dataclass(frozen=True)
+@dataclass(frozen=True, init=False)
 class NormalizedResponse:
  text: str
  tool_calls: tuple[ToolCall, ...]
  usage: UsageStats
  raw_response: Any
 
+ def __init__(
+  self,
+  text: str,
+  tool_calls: tuple[ToolCall, ...] = (),
+  usage: UsageStats | None = None,
+  raw_response: Any = None,
+  usage_input_tokens: int | None = None,
+  usage_output_tokens: int | None = None,
+  usage_cache_read_tokens: int | None = None,
+  usage_cache_creation_tokens: int | None = None,
+ ) -> None:
+  if usage is None:
+   usage = UsageStats(
+    input_tokens=usage_input_tokens if usage_input_tokens is not None else 0,
+    output_tokens=usage_output_tokens if usage_output_tokens is not None else 0,
+    cache_read_tokens=usage_cache_read_tokens if usage_cache_read_tokens is not None else 0,
+    cache_creation_tokens=usage_cache_creation_tokens if usage_cache_creation_tokens is not None else 0,
+   )
+  object.__setattr__(self, "text", text)
+  object.__setattr__(self, "tool_calls", tool_calls)
+  object.__setattr__(self, "usage", usage)
+  object.__setattr__(self, "raw_response", raw_response)
+
  def to_legacy_dict(self) -> JsonValue:
   return {
    "text": self.text,