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-446-retractions-b.md

@@ -1,45 +1,31 @@
 ---
 id: 5900f52c1000cf542c51003d
-challengeType: 5
 title: 'Problem 446: Retractions B'
+challengeType: 5
 forumTopicId: 302118
 ---
 
-## Description
-<section id='description'>
-For every integer n>1, the family of functions fn,a,b  is defined
-by fn,a,b(x)≡ax+b mod n for a,b,x integer and  0<a<n, 0≤b<n, 0≤x<n.
-We will call fn,a,b a retraction if fn,a,b(fn,a,b(x))≡fn,a,b(x) mod n for every 0≤x<n.
-Let R(n) be the number of retractions for n.
+# --description--
 
+For every integer n>1, the family of functions fn,a,b is defined
 
-F(N)=∑R(n4+4) for 1≤n≤N.
-F(1024)=77532377300600.
+by fn,a,b(x)≡ax+b mod n for a,b,x integer and 0
+
+F(N)=∑R(n4+4) for 1≤n≤N. F(1024)=77532377300600.
 
 Find F(107) (mod 1 000 000 007)
-</section>
 
-## Instructions
-<section id='instructions'>
+# --hints--
 
-</section>
-
-## Tests
-<section id='tests'>
-
-```yml
-tests:
-  - text: <code>euler446()</code> should return 907803852.
-    testString: assert.strictEqual(euler446(), 907803852);
+`euler446()` should return 907803852.
 
+```js
+assert.strictEqual(euler446(), 907803852);
 ```
 
-</section>
+# --seed--
 
-## Challenge Seed
-<section id='challengeSeed'>
-
-<div id='js-seed'>
+## --seed-contents--
 
 ```js
 function euler446() {
@@ -50,17 +36,8 @@ function euler446() {
 euler446();
 ```
 
-</div>
-
-
-
-</section>
-
-## Solution
-<section id='solution'>
+# --solutions--
 
 ```js
 // solution required
 ```
-
-</section>