lang: Include `pubkey!` macro in `prelude`

[acheroncrypto]

Problem

pubkey! macro added in https://github.com/coral-xyz/anchor/pull/3021 is not included in the anchor_lang::prelude.

Summary of changes

• Add pubkey! macro in anchor_lang::prelude
• Replace Pubkey::from_str to pubkey! macro in tests

[vercel[bot]]

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