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/string/escapes.wren

@@ -2,6 +2,7 @@
 System.print("\"")     // expect: "
 System.print("\\")     // expect: \
 System.print("(\n)")   // expect: (
-                   // expect: )
+                       // expect: )
+System.print("\%")     // expect: %
 
 // TODO: Non-printing escapes like \t.