feat: implement string interpolation with %(expr) syntax in compiler and core library

Add lexer support for `TOKEN_INTERPOLATION` to split string literals at interpolation points, introduce `MAX_INTERPOLATION_NESTING` limit of 8, and compile interpolated strings by emitting calls to `String.interpolate_()`. Optimize list and map literal construction with new `addCore_` primitives to reduce stack churn. Update `String`, `List`, and `Map` `toString` methods in core library to use interpolation syntax, and migrate all benchmark and test files from explicit concatenation to interpolated strings.

test/language/method/newlines.wren

@@ -1,7 +1,7 @@
 class Foo {
   construct new() {}
-  method(a, b) { "method " + a + " " + b }
-  [a, b] { "subscript " + a + " " + b }
+  method(a, b) { "method %(a) %(b)" }
+  [a, b] { "subscript %(a) %(b)" }
 }
 
 var foo = Foo.new()

test/language/method/operators.wren

@@ -1,20 +1,20 @@
 class Foo {
   construct new() {}
 
-  +(other) { "infix + " + other }
-  -(other) { "infix - " + other }
-  *(other) { "infix * " + other }
-  /(other) { "infix / " + other }
-  %(other) { "infix % " + other }
-  <(other) { "infix < " + other }
-  >(other) { "infix > " + other }
-  <=(other) { "infix <= " + other }
-  >=(other) { "infix >= " + other }
-  ==(other) { "infix == " + other }
-  !=(other) { "infix != " + other }
-  &(other) { "infix & " + other }
-  |(other) { "infix | " + other }
-  is(other) { "infix is " + other }
+  +(other) { "infix + %(other)" }
+  -(other) { "infix - %(other)" }
+  *(other) { "infix * %(other)" }
+  /(other) { "infix / %(other)" }
+  %(other) { "infix \% %(other)" }
+  <(other) { "infix < %(other)" }
+  >(other) { "infix > %(other)" }
+  <=(other) { "infix <= %(other)" }
+  >=(other) { "infix >= %(other)" }
+  ==(other) { "infix == %(other)" }
+  !=(other) { "infix != %(other)" }
+  &(other) { "infix & %(other)" }
+  |(other) { "infix | %(other)" }
+  is(other) { "infix is %(other)" }
 
   ! { "prefix !" }
   ~ { "prefix ~" }

test/language/method/static.wren

@@ -3,8 +3,8 @@ class Foo {
   bar { "on instance" }
   static bar { "on metaclass" }
 
-  bar(arg) { "on instance " + arg }
-  static bar(arg) { "on metaclass " + arg }
+  bar(arg) { "on instance %(arg)" }
+  static bar(arg) { "on metaclass %(arg)" }
 }
 
 System.print(Foo.new().bar)        // expect: on instance

test/language/method/subscript_operators.wren

@@ -1,11 +1,11 @@
 class Foo {
   construct new() {}
-  [a] { "1-subscript " + a }
-  [a, b] { "2-subscript " + a + " " + b }
-  [a, b, c] { "3-subscript " + a + " " + b + " " + c }
-  [a]=(value) { "1-subscript setter " + a + " = " + value }
-  [a, b]=(value) { "2-subscript setter " + a + " " + b + " = " + value }
-  [a, b, c]=(value) { "3-subscript setter " + a + " " + b + " " + c + " = " + value }
+  [a] { "1-subscript %(a)" }
+  [a, b] { "2-subscript %(a) %(b)" }
+  [a, b, c] { "3-subscript %(a) %(b) %(c)" }
+  [a]=(value) { "1-subscript setter %(a) = %(value)" }
+  [a, b]=(value) { "2-subscript setter %(a) %(b) = %(value)" }
+  [a, b, c]=(value) { "3-subscript setter %(a) %(b) %(c) = %(value)" }
 }
 
 var foo = Foo.new()