Update smart contract to support onramp

[SarahSync]

User Story

Add the details of this issue from the user's POV

Acceptance Criteria

1. Successful order settlement with fee deductions
   GIVEN an order with defined sender and protocol fees
   WHEN the processSettlement function is called on the Gateway contract
   THEN the contract should transfer the correct token amount to the recipient
   AND deduct sender and protocol fees accurately
   AND emit the ProcessSettlement event with correct parameters

2. Settlement fails due to insufficient balance
   GIVEN an order where the sender balance is insufficient for the total amount plus fees
   WHEN processSettlement is executed
   THEN the transaction should revert with an appropriate error message
   AND no settlement or event emission should occur

Tech Details
#66

• Implemented processSettlement function in Gateway contract to handle order settlements, including sender fees and protocol fees.
• Added ProcessSettlement event to IGateway interface and emitted it during settlement.
• Updated Gateway contract to check for sender fees and protocol fees during token transfers.
• Enhanced order struct to store additional settlement details.
• Created comprehensive tests for processSettlement functionality, covering various scenarios including fee deductions.
• Updated relevant interfaces and mock contracts to support new functionality.

Notes/Assumptions

• Notes or assumption that has to remain constant.

Open Questions