Resolve single_match_else pedantic clippy lint in code generator

    warning: you seem to be trying to use `match` for destructuring a single pattern. Consider using `if let`
       --> src/parse.rs:146:33
        |
    146 |                       let punct = match introspect_type(last_arg(&last.arguments), lookup) {
        |  _________________________________^
    147 | |                         types::Type::Token(s) => s,
    148 | |                         _ => panic!(),
    149 | |                     };
        | |_____________________^ help: try: `if let types::Type::Token(s) = introspect_type(last_arg(&last.arguments), lookup) { s } else { panic!() }`
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#single_match_else
        = note: `-W clippy::single-match-else` implied by `-W clippy::pedantic`
        = help: to override `-W clippy::pedantic` add `#[allow(clippy::single_match_else)]`

codegen/src/parse.rs

@@ -143,11 +143,11 @@ fn introspect_type(item: &syn::Type, lookup: &Lookup) -> types::Type {
                 }
                 "Punctuated" => {
                     let nested = introspect_type(first_arg(&last.arguments), lookup);
-                    let punct = match introspect_type(last_arg(&last.arguments), lookup) {
-                        types::Type::Token(s) => s,
-                        _ => panic!(),
+                    let types::Type::Token(punct) =
+                        introspect_type(last_arg(&last.arguments), lookup)
+                    else {
+                        panic!()
                     };
-
                     types::Type::Punctuated(types::Punctuated {
                         element: Box::new(nested),
                         punct,