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/setter/associativity.wren

@@ -1,7 +1,7 @@
 class Foo {
   new(value) { _value = value }
   toString { _value }
-  bar = value {
+  bar=(value) {
     _value = value
     return value
   }

test/setter/grouping.wren

@@ -1,5 +1,5 @@
 class Foo {
-  bar = value { value }
+  bar=(value) { value }
 }
 
 var foo = new Foo

test/setter/infix_operator.wren

@@ -1,5 +1,5 @@
 class Foo {
-  bar = value { value }
+  bar=(value) { value }
 }
 
 var foo = new Foo

test/setter/instance.wren

@@ -1,5 +1,5 @@
 class Foo {
-  bar = value {
+  bar=(value) {
     IO.print(value)
   }
 }

test/setter/is.wren

@@ -1,5 +1,5 @@
 class Foo {
-  bar = value { value }
+  bar=(value) { value }
 }
 
 var foo = new Foo

test/setter/prefix_operator.wren

@@ -1,5 +1,5 @@
 class Foo {
-  bar = value { value }
+  bar=(value) { value }
 }
 
 var foo = new Foo

test/setter/result.wren

@@ -1,5 +1,5 @@
 class Foo {
-  bar = value { "result" }
+  bar=(value) { "result" }
 }
 
 var foo = new Foo

test/setter/same_name_as_method.wren

@@ -1,5 +1,5 @@
 class Foo {
-  bar = value { IO.print("set") }
+  bar=(value) { IO.print("set") }
   bar { IO.print("get") }
 }
 

test/setter/static.wren

@@ -1,5 +1,5 @@
 class Foo {
-  static bar = value {
+  static bar=(value) {
     IO.print(value)
   }
 }