Reasons:

• I don't think there would ever be used one without the other
• AxelarGatewayDestionation is axelar executable. That prevents AxelarBase from exposing gateway(), so currently AxelarGatewaySource doesn't have that getter

Proposal:

• Merge AxelarGatewaySource and AxelarGatewayDestination into a single contract called AxelarGatewayAdaptor
• Remove AxelarGatewayDuplex
• Use AxelarGatewayAdaptor instead of AxelarGatewayDuplex

Alternative names

• AxelarGatewayAdaptor
• AxelarERC7802Adaptor
• AxelarERC7802Gateway