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[jordaaash]

This PR completes SIWS by combining several other PRs that were merged to an alpha branch for final production release.

• https://github.com/solana-labs/wallet-standard/pull/12
• https://github.com/solana-labs/wallet-standard/pull/20
• https://github.com/solana-labs/wallet-standard/pull/21
• https://github.com/solana-labs/wallet-standard/pull/22
• https://github.com/solana-labs/wallet-standard/pull/23
• https://github.com/solana-labs/wallet-standard/pull/26
• https://github.com/solana-labs/wallet-standard/pull/28
• https://github.com/solana-labs/wallet-standard/pull/29