Add Aptos exact scheme

[jillxuu]

Description

this aptos scheme supports both standard transactions where the client pays gas and sponsored transactions where the facilitator pays gas fees, with a future enhancement planned to use a custom x402 payment contract that validates amounts and emits on-chain events for better payment tracking.

Tests

Checklist

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

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1

[vercel[bot]]

@jillxuu is attempting to deploy a commit to the Coinbase Team on Vercel.

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