Performance: Optimize historical performance fetching & implement backend caching to avoid rate-limiting

[yashvi-3106]

Description

This PR optimizes the student history loading process. Previously, loading a student's analytics profile required fetching up to 365 daily snapshot files from the remote data repository in chunks of 100 HTTP requests. By transitioning to a single, pre-generated historical user data file (historical-user-data/username.json) per student, we reduce the network load from $O(\text{days})$ to a single $O(1)$ JSON request.

Linked Issue

Fixes #154

Changes Made

• Added scripts/bootstrap-user-history.js: A one-time bootstrap script that parses all existing daily snapshot files under data/daily/ and compiles historical records into individual user history files under data/historical-user-data/.
• Modified scripts/sync-leaderboard.js: Integrates incremental history updates into the sync cron job. It appends the latest solved counts (easy, medium, hard) to each user's history file during daily synchronization.
• Modified scripts/fetch-student-info.js: Refactored the retrieval logic to load the single user history file directly. It searches the local directory first for development environments, and falls back to a raw GitHub query in production.

Type of Change

• Bug fix
• New feature
• UI/Visual update
• Documentation update
• Refactor

Testing

I successfully tested the modifications locally:

• Migration test: Ran the bootstrap script on a local clone of the data repository to successfully generate user history files for 121 users from 342 daily snapshots.

• Sync test: Executed the synchronization script and confirmed the stats correctly appended to the user-specific history files under the new directory.

• API Fetch test: Verified the refactored fetchStudentHistory successfully queries the Vercel API and reads history files in ~1.1 seconds with zero console errors.

• Tested locally

• Tested on mobile viewport (if applicable)

• No console errors introduced

Checklist

• My code follows the project's coding style
• I have formatted my code locally by running npx prettier --write . before submitting
• I am submitting my PR from a dedicated branch, not the main branch
• I have performed a self-review of my code
• My changes generate no new warnings or errors
• I have updated documentation if required
• I have linked the relevant issue

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[yashvi-3106]

@jagdish-15 i have linked this pr you can review it!