`Template`s should be able to collect `Tool`s from arguments

Currently `Template`s only collect `Tool`s from their enclosing scope, i.e. if a `Tool` or an `Agent` is passed as an argument to a `Template` then it is not included in the list of tools passed to the underlying LLM API. However, there's no reason to treat this case differently; arguments are simply another layer in the lexical scope of the body of the `Template`.