feat: require parentheses around operator and setter method parameters in Wren

Enforce syntactic requirement for parentheses in operator method signatures (e.g., `+(other)` instead of `+ other`) and setter definitions (e.g., `bar=(value)` instead of `bar = value`). Update the compiler's `infixSignature`, `mixedSignature`, and `namedSignature` functions to consume explicit `(` and `)` tokens around parameter names. Migrate all built-in core library operator definitions and test fixtures to the new parenthesized syntax.

test/constructor/infix_class_expression.wren

@@ -1,5 +1,5 @@
 class Foo {
-  + other { "Foo " + other }
+  +(other) { "Foo " + other }
 }
 
 IO.print(new Foo + "value") // expect: Foo value