fix: number of stakers from v3 indexer

[gluneau]

Pull Request Summary

fixes the number of stakers on the dashboard and pulls them from v3 indexer

Check list

• [ ] contains breaking changes
• [ ] adds new feature
• [x] modifies existing feature (bug fix or improvements)
• [ ] relies on other tasks
• [ ] documentation changes
• [ ] tested on mobile devices

[github-actions[bot]]

Visit the preview URL for this PR (updated for commit 7250960):

https://astar-apps--pr1212-fix-dashboard-staker-op40iooa.web.app

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