fix: add 8s fetch timeouts to CodeChef, Codeforces, GitHub REST, and GitHub GraphQL services

[rishab11250]

Description

Added AbortController-based 8-second fetch timeouts to all external API services that were missing them. LeetCode service already had this pattern (8s timeout) — this PR applies the same pattern to the remaining services.

Changes

• src/services/codechef.service.js — Added 8s AbortController timeout to getCodeChefData()
• src/services/codeforces.service.js — Added shared 8s AbortController timeout to both parallel fetches in getCodeforcesData()
• src/services/github.service.js — Added 8s timeouts to fetchUserProfile(), fetchUserRepos() (per pagination page), and updated fetchAvatarDataUri() timeout from 4s → 8s
• src/services/github-graphql.service.js — Added 8s AbortController timeout with try/catch to fetchContributionData()

Pattern used (consistent across all services)

• AbortController + setTimeout(() => controller.abort(), 8000)
• signal: controller.signal in fetch options
• clearTimeout(timeout) after successful response
• Catch block translates AbortError → user-friendly timeout message (e.g. "CodeChef API timeout")

Testing

• All 12 existing unit tests pass (npm run test:unit)

Closes #100

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[SamXop123]

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