f4 library Null safety

Future helper methods & classes.

Classes

AbortController
Abort controller that optionally receives onAbort callback in which case an AbortError doesn't get thrown by the Future.
AbortSignal
Abort cancellation signal
F4
A class container of all static Future method helpers.
ReflectedFuture
A class representation of a reflected Future.

Exceptions / Errors

AbortError
Custom Abort error.
RejectionError
Custom rejection error.