Consider using null safety

[RedstoneMedia]

Describe the solution you'd like
It would be useful, if this library would use sound null safety, like basically every new library does nowadays.
This is annoying since flutter forces you to explicitly disable null safety, if ANY dependency does not use it, which means that all the work that I already put in, to make my code null safe is completely invalidated by this library.

Describe alternatives you've considered
I have considered using other dependencies such as opencv_4, however none of the dependencies support the feature that I need (warpPerspectiveTransform).

[turbolux]

Hope to improve