chore: enable eslint cache

[karamaru-alpha]

Summary

I've enabled caching in ESLint.

• The default --cache-location is .eslintcache, but to avoid adding files to the root directory, I've changed it to node_modules/.cache/eslint/.eslintcache using find-cache-dir as a reference.
• The default --cache-strategy is metadata, which detects differences based on file timestamps. If caching the cache file in GitHub Actions, it's necessary to change to content to detect differences based on file hash values, but since it's currently only being executed locally, I've left it as metadata.

Screenshots

Before	After(cached)
13.2s $ time pnpm lint > pnpm lint 21.11s user 1.32s system 169% cpu 13.211 total	1.2s $ time pnpm lint > pnpm lint 1.19s user 0.3w8s system 123% cpu 1.270 total

Checklist

[!IMPORTANT]
Please review the checklist below before submitting your pull request.

• [ ] This change requires a documentation update, included: Dify Document
• [x] I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• [x] I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• [x] I've updated the documentation accordingly.
• [x] I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods