Client is the Lambda Runtime Interface client.
It is implemented as a singleton whereby
always returns the already instantiated client.
Invocation error occurs when there has been an
error in the invocation of a handlers. It dynamically
wraps the inner error and attaches the
track it along the event.
Invocation result is the result that the invoked handler
returns and is posted to the Lambda Runtime Interface.
Next invocation data wraps the data from the
invocation endpoint of the Lambda Runtime Interface.