[hot fix] Use Beaconcha.in endpoint for total ETH staked

[wackerow]

Description

• Removes usage of Dune Analytics API for fetching total ETH staked
• Adds isolated lib/api fetch utility to get "eligible ETH" from Beaconcha.in "epoch" endpoint
• Implement new fetch value on homepage and /enterprise page
• Update /staking fetch to use same pattern (eligibleether value instead of effective_balances_sum_wei) to align with homepage, /enterprise page, and Beaconcha.in homepage

Related Issue

Production deploys breaking as a result of hitting Dune API request limits

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