Highlight variables in string interpolation

[anilraghuramu]

I'm not sure if this is a theme issue or something rustic can fix, is there a way to highlight variables in a format string.
For example here:

let code = "if let Some({arg_name}) = &self.{arg_name} {{ bytes.extend_from_slice(&serialize_{arg_ty}(&{arg_name})); }}"

I'd like arg_name and arg_ty to be highlighted.