Feature: Add Time-Limited Challenges

[Anushka-Pote]

Is your feature request related to a problem? Please describe.
Description: Add a time-limited challenge feature where users can compete to solve a LeetCode problem within a specific time frame (e.g., 30 minutes).

Describe the solution you'd like
Set up a /challenge command where users can opt into the timed challenge.
Select a random problem (or based on difficulty) and display it.
Start a countdown timer for each user, and when the timer ends, check whether they submitted a solution via their LeetCode account

Additional context
This feature gamifies the experience, adding time pressure to simulate real coding contests or job interviews. It would increase user engagement and add an element of fun.

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[github-actions]

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