fix(toolset): enhance additional_headers input types

Author: anubhav756

packages/toolbox-adk/src/toolbox_adk/toolset.py

@@ -34,7 +34,7 @@ def __init__(
         toolset_name: Optional[str] = None,
         tool_names: Optional[List[str]] = None,
         credentials: Optional[CredentialConfig] = None,
-        additional_headers: Optional[Dict[str, str]] = None,
+        additional_headers: Optional[Dict[str, Union[str, Callable[[], str], Callable[[], Awaitable[str]]]]] = None,
         bound_params: Optional[Mapping[str, Union[Callable[[], Any], Any]]] = None,
         pre_hook: Optional[Callable[[ToolboxContext], Awaitable[None]]] = None,
         post_hook: Optional[Callable[[ToolboxContext], Awaitable[None]]] = None,
@@ -46,7 +46,7 @@ def __init__(
             toolset_name: The name of the remote toolset to load.
             tool_names: Specific tool names to load (alternative to toolset_name).
             credentials: Authentication configuration.
-            additional_headers: Extra static headers (e.g. for proxy auth).
+            additional_headers: Extra headers (static or dynamic).
             bound_params: Parameters to bind globally to loaded tools.
             pre_hook: Hook to run before every tool execution.
             post_hook: Hook to run after every tool execution.