perf: cache TypeAdapter instances across tool invocations

Author: yuvrajangadsingh

src/google/adk/tools/function_tool.py

@@ -90,6 +90,7 @@ def __init__(
     self.func = func
     self._ignore_params = ['tool_context', 'input_stream']
     self._require_confirmation = require_confirmation
+    self._type_adapter_cache: dict[Any, pydantic.TypeAdapter] = {}
 
   @override
   def _get_declaration(self) -> Optional[types.FunctionDeclaration]:
@@ -154,7 +155,11 @@ def _preprocess_args(
       # Validate and coerce all annotated types using TypeAdapter.
       # This handles primitives, enums, Pydantic models, and container types.
       try:
-        adapter = pydantic.TypeAdapter(target_type)
+        if target_type not in self._type_adapter_cache:
+          self._type_adapter_cache[target_type] = pydantic.TypeAdapter(
+              target_type
+          )
+        adapter = self._type_adapter_cache[target_type]
         converted_args[param_name] = adapter.validate_python(
             args[param_name]
         )