Feat: add new Markdown parser (#39800)

and change all the challenges to new `md` format.

curriculum/challenges/english/10-coding-interview-prep/project-euler/problem-427-n-sequences.md

@@ -1,46 +1,35 @@
 ---
 id: 5900f5181000cf542c51002a
-challengeType: 5
 title: 'Problem 427: n-sequences'
+challengeType: 5
 forumTopicId: 302097
 ---
 
-## Description
-<section id='description'>
+# --description--
+
 A sequence of integers S = {si} is called an n-sequence if it has n elements and each element si satisfies 1 ≤ si ≤ n. Thus there are nn distinct n-sequences in total.
+
 For example, the sequence S = {1, 5, 5, 10, 7, 7, 7, 2, 3, 7} is a 10-sequence.
 
-For any sequence S, let L(S) be the length of the longest contiguous subsequence of S with the same value.
-For example, for the given sequence S above, L(S) = 3, because of the three consecutive 7's.
+For any sequence S, let L(S) be the length of the longest contiguous subsequence of S with the same value. For example, for the given sequence S above, L(S) = 3, because of the three consecutive 7's.
 
 Let f(n) = ∑ L(S) for all n-sequences S.
 
 For example, f(3) = 45, f(7) = 1403689 and f(11) = 481496895121.
 
-Find f(7 500 000) mod 1 000 000 009.
-</section>
+Find f(7 500 000) mod 1 000 000 009.
 
-## Instructions
-<section id='instructions'>
+# --hints--
 
-</section>
-
-## Tests
-<section id='tests'>
-
-```yml
-tests:
-  - text: <code>euler427()</code> should return 97138867.
-    testString: assert.strictEqual(euler427(), 97138867);
+`euler427()` should return 97138867.
 
+```js
+assert.strictEqual(euler427(), 97138867);
 ```
 
-</section>
+# --seed--
 
-## Challenge Seed
-<section id='challengeSeed'>
-
-<div id='js-seed'>
+## --seed-contents--
 
 ```js
 function euler427() {
@@ -51,17 +40,8 @@ function euler427() {
 euler427();
 ```
 
-</div>
-
-
-
-</section>
-
-## Solution
-<section id='solution'>
+# --solutions--
 
 ```js
 // solution required
 ```
-
-</section>