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()