Refactor all fetchers to use fetchRetry

[pettinarip]

Summary

• Replace plain fetch() with fetchRetry() across all 26 data-layer fetchers for automatic retry on transient HTTP errors (408, 409, 429, 500-599)
• Remove custom retry() wrapper usage in fetchGitHub and fetchNpmJs, consolidating retry logic into the shared fetchRetry utility
• Delete the now-unused src/lib/utils/fetch.ts (old retry/sleep utilities)
• Add per-caller override support to fetchRetry for custom retry strategies (e.g. "headers" strategy for APIs with Retry-After)

Details

• fetchRetry wraps Trigger.dev's retry.fetch with exponential backoff (3 attempts) on 408, 409, 429, and 500-599
• GitHub-specific 403 rate-limit handling preserved in fetchGitHubContributors and fetchGitHistory (GitHub uses 403, not 429)
• Inter-batch pacing delays preserved where they existed (GitHub GraphQL 1s, npm 15s)
• sleep utility exported from fetchRetry.ts for shared use

Test plan

• TypeScript compiles cleanly (npx tsc --noEmit)
• ESLint + Prettier pass (via pre-commit hooks)
• Verify fetchers succeed in Trigger.dev dev environment
• Monitor first production run for any regression in data fetching

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[wackerow]

Looks good!

[wackerow]

Could consider leaving this back in the fetch util, unless it needs to be inside data-layer dir.. not a blocker