Update `tool.Invoke()` to return type `any` instead of `[]any`.
Toolbox return a map with the `results` key, and the SDK reads the
string from the key. So this won't break existing SDK implementation.
Fixes#870
Allow Toolbox server to automatically update when users modify their
tool configuration file(s), instead of requiring a restart.
This feature is automatically enabled, but can be turned off with the
flag `--disable-reload`.
