evict invalid stakes cache entries on epoch boundaries

Active on mainnet-beta (epoch 271), testnet (epoch 276) and devnet (epoch 252).

Introduced in solana-labs/solana PR #21654.

Feature id EMX9Q7TVFAmQ9V1CggAkhMzhXSg8ECp7fHrWQX2G1chf.

Vortex

• Consensus leaderboard
• Fees leaderboard
• Validators
• Stake pools
• Decentralization
• Client versions
• Cluster status
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• SIMDs
• Activity
• API and AI usage