[Orca] Create token account for referral address

[0xh3rman]

No description provided.

[gemini-code-assist]

Summary of Changes

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This pull request refactors the referral fee processing within the Orca Whirlpool provider to ensure robust handling of referral payments. By modifying the instruction generation to return an array, it now idempotently creates the referrer's associated token account for legacy SPL tokens before transferring the fee, enhancing reliability and compatibility with Solana's token standards. This change streamlines the referral mechanism without altering the core swap functionality.

Highlights

• Referral Instruction Handling: The method responsible for building referral instructions, buildReferralInstruction, has been renamed to buildReferralInstructions and now returns an array of TransactionInstruction objects instead of a single instruction or null. This allows for more complex referral logic.
• Associated Token Account Creation: For legacy SPL tokens, the referral instruction logic now includes an createAssociatedTokenAccountIdempotentInstruction. This ensures that the referrer's associated token account is created if it doesn't already exist, before attempting to transfer the referral fee.
• Native SOL and Token-2022 Program Handling: The updated logic correctly handles native SOL transfers by returning a SystemProgram.transfer instruction within an array. For Token-2022 program mints or zero referral amounts, an empty array of instructions is returned, maintaining previous behavior for these cases.
• Test Suite Updates: Corresponding test cases in provider.test.ts have been updated to reflect the change in return type and behavior, now asserting for arrays of instructions and the inclusion of the associated token account creation instruction.

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[gemini-code-assist]

Code Review

This pull request correctly implements the creation of an associated token account for the referral address when needed. The changes are well-structured, with the logic encapsulated in the buildReferralInstructions method. The use of createAssociatedTokenAccountIdempotentInstruction is appropriate for this purpose. The related tests have been updated accordingly to reflect these changes. I have one suggestion to improve the robustness of the tests.