chore(security): fix blockhash call for a valid previous block hash

[qtipbera]

https://semgrep.dev/orgs/berachain/findings/207695913

[Copilot]

Pull Request Overview

This PR fixes a security issue in the Multicall3 contract where blockhash(block.number) was incorrectly used, which always returns 0 according to Ethereum specifications. The fix changes it to use blockhash(block.number - 1) to get a valid previous block hash.

• Replace incorrect blockhash(block.number) call with blockhash(block.number - 1)
• Add explanatory comments about the blockhash behavior and safety considerations

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[Copilot]

Pull Request Overview

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