Adds cache tokens to usage type

Author: Workshop Participant

src/strands/types/event_loop.py

@@ -5,18 +5,22 @@
 from typing_extensions import TypedDict
 
 
-class Usage(TypedDict):
+class Usage(TypedDict, total=False):
     """Token usage information for model interactions.
 
     Attributes:
         inputTokens: Number of tokens sent in the request to the model..
         outputTokens: Number of tokens that the model generated for the request.
         totalTokens: Total number of tokens (input + output).
+        cacheReadInputTokens: Number of tokens read from cache.
+        cacheWriteInputTokens: Number of tokens written to cache.
     """
 
     inputTokens: int
     outputTokens: int
     totalTokens: int
+    cacheReadInputTokens: int
+    cacheWriteInputTokens: int
 
 
 class Metrics(TypedDict):