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/break/nested_for_loop.wren

@@ -1,9 +1,9 @@
 for (i in 0..2) {
-  System.print("outer " + i.toString)
+  System.print("outer %(i)")
   if (i > 1) break
 
   for (j in 0..2) {
-    System.print("inner " + j.toString)
+    System.print("inner %(j)")
     if (j > 1) break
   }
 }

test/language/break/nested_while_loop.wren

@@ -1,11 +1,11 @@
 var i = 0
 while (true) {
-  System.print("outer " + i.toString)
+  System.print("outer %(i)")
   if (i > 1) break
 
   var j = 0
   while (true) {
-    System.print("inner " + j.toString)
+    System.print("inner %(j)")
     if (j > 1) break
 
     j = j + 1