fix: Use tokens= instead of usage= on LDAIMetrics constructors

- bedrock_example.py and langgraph_agent_example.py both passed usage= to
  LDAIMetrics(...) constructors, which raises TypeError on Python AI SDK
  0.16+. The dataclass field is tokens.

Refs AIC-2383

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: jsonbailey

getting_started/bedrock/converse/bedrock_example.py

@@ -34,7 +34,7 @@ def get_bedrock_metrics(response):
 
     duration_ms = response.get("metrics", {}).get("latencyMs")
 
-    return LDAIMetrics(success=success, usage=usage, duration_ms=duration_ms)
+    return LDAIMetrics(success=success, tokens=usage, duration_ms=duration_ms)
 
 # Set sdk_key to your LaunchDarkly SDK key.
 sdk_key = os.getenv('LAUNCHDARKLY_SDK_KEY')

getting_started/langgraph/react_agent/langgraph_agent_example.py

@@ -33,7 +33,7 @@ def map_provider_to_langchain(provider_name):
 def get_langgraph_metrics(response):
     """Extract aggregated metrics from a LangGraph agent response."""
     messages = response.get("messages", [])
-    return LDAIMetrics(success=True, usage=sum_token_usage_from_messages(messages))
+    return LDAIMetrics(success=True, tokens=sum_token_usage_from_messages(messages))
 
 def get_weather(city: str) -> str:
     """Get the weather for a given city."""