add prompt language option

example/src/quiz.toml

@@ -21,6 +21,7 @@ For example, you can make a mutable variable `x` by writing: `let mut x = 1`.
 
 [[questions]]
 type = "Tracing"
+prompt.language="rust"
 prompt.program = """
 fn main() {
   let x = 1;

js/packages/quiz-schema/src/tracing.ts

@@ -3,6 +3,8 @@ import { QuestionFields } from "./common";
 export interface TracingPrompt {
   /** The contents of the program to trace */
   program: string;
+
+  language?: string;
 }
 
 export interface TracingAnswer {

js/packages/quiz/src/questions/tracing.tsx

@@ -30,7 +30,11 @@ export let TracingMethods: QuestionMethods<TracingPrompt, TracingAnswer> = {
         {/* If the program does not pass, indicate the last line number involved in the
         compiler error. */}
       </p>
-      <Snippet snippet={prompt.program} lineNumbers />
+      <Snippet
+        language={prompt.language}
+        snippet={prompt.program}
+        lineNumbers
+      />
     </>
   ),