Named-only arguments in templates

Given that our implementation of named template parameters largely mirrors Python, one feature we discussed but chose not to implement is the concept of named-only arguments:
https://peps.python.org/pep-3102/

**Python Syntax**
`def foo(a, b=1, * c="cat")`

Here `a` and `b` can be supplied positionally _or_ by name, but `c` can only be supplied by name. The `*` character in the argument list delineates the positional-or-named arguments from the named-only arguments, and the named-only arguments must come at the end of the signature.