feat: implement IO.read method with stdin input buffer and prompt support

Add static `IO.read(prompt)` method to the IO class that writes the prompt to stdout
and reads a line from stdin into a 1024-byte buffer. The C implementation uses
`fgets` for input and returns the string via `wrenReturnString`. The Wren wrapper
calls `IO.write` for the prompt before delegating to the native `IO.read` method.

builtin/io.wren

@@ -78,4 +78,9 @@ class IO {
     IO.writeString_(obj.toString)
     return obj
   }
+
+  static read(prompt) {
+    IO.write(prompt)
+    return IO.read
+  }
 }