Add CPI inner instruction scanning to charge scheme for smart wallet support

[0xultravioleta]

Summary

Smart wallets on Solana (Squads, Crossmint, SWIG) route SPL token transfers through cross-program invocations (CPI). The actual TransferChecked instruction lives inside an inner instruction, not at the top level of the transaction.

The @faremeter/x-solana-settlement scheme already handles this pattern — its isValidTransferTransaction, extractTransferData, and isValidMemo functions all scan transaction.meta.innerInstructions when top-level matching fails. This PR brings the same capability to the charge scheme in packages/payment-solana.

Changes

packages/payment-solana/src/charge/server.ts

• fetchConfirmedTransaction() now returns innerInstructions and staticAccountKeys from the on-chain transaction meta alongside the decompiled message
• The push-mode ("signature" payload) path passes inner instructions to verifyChargeTransaction

packages/payment-solana/src/charge/verify.ts

• VerifyChargeTransactionArgs accepts optional innerInstructions and staticAccountKeys
• New findTransferInInnerInstructions() function scans CPI inner instructions for TransferChecked as a fallback when no top-level match is found
• Same security checks as the top-level path: mint must match, destination must be the correct ATA, amount must match, authority must not be the fee payer, exactly one matching transfer allowed
• Supports both spl_token and spl_token_2022 programs

Backward compatibility

Existing top-level transfers still match first. The inner instruction path only activates as a fallback when the existing top-level scan returns no match. All existing exact/verify.test.ts tests pass unchanged (36/36).

Context

• Closes Extend CPI inner instruction scanning to exact and charge schemes for smart wallet support #150
• Related: PR feat: swig solana wallet plugin #86 (Swig smart wallet plugin) — CPI scanning complements the Swig integration
• The CPI inner instruction pattern is documented in the Solana CPI docs