Refactor SVM client and verification logic to remove create ATA instruction

[notorious-d-e-v]

Description

Refactor SVM client and verification logic to remove create ATA instruction handling

• Removed create associated token account (ATA) instruction logic from SVM client and tests.
• Updated transfer instruction handling to assume destination ATA exists.
• Adjusted verification functions to reflect changes in instruction expectations.
• Cleaned up related test cases to remove references to create ATA instructions.

Tests

Updated existing tests.

Checklist

• [x] I have formatted and linted my code
• [x] All new and existing tests pass
• [x] My commits are signed (required for merge) -- you may need to rebase if you initially pushed unsigned commits

[cb-heimdall]

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[vercel[bot]]

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[amilz]

IMO this is a good change. Facilitator should be responsible for keeping their ATA open. Might be worth documenting expected transaction structure in x402-specification.md or a readme in typescript/packages/x402/src/schemes/exact/svm/facilitator/. This hits on some of the elements of #421 -- I think we could tackle the rest of that after this merges.

[notorious-d-e-v]

Thanks, agreed! You're right, should update the docs.

Ideally there will be a way for facilitators to help merchants set up their ATA. It could also be a sponsored tx where the merchant pays in USDC.

But for now it's simplest to just remove it.