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/io/stdin/read_line.wren

@@ -1,9 +1,9 @@
 import "io" for Stdin
 
 System.write("> ")
-System.print("1 " + Stdin.readLine())
+System.print("1 %(Stdin.readLine())")
 System.write("> ")
-System.print("2 " + Stdin.readLine())
+System.print("2 %(Stdin.readLine())")
 
 // stdin: first
 // stdin: second