The core library of ff_annotation_route, support both null-safety and non-null-safety.

• null-safety

environment:
  sdk: '>=2.12.0 <3.0.0'
dependencies:
  ff_annotation_route_core: ^2.0.0

• non-null-safety

environment:
  sdk: '<2.12.0'
dependencies:
  ff_annotation_route_core: ^2.0.1-non-null-safety