Add null-safety support

[paurakhsharma]

Thank you for this great package,
Can you please add null-safety for it? I can create a PR if you are busy.

[aaronkelton]

This package is still not null-safe. Someone was even kind enough to open a PR with the necessary changes, but they haven't merged it. #25

Error: Cannot run with sound null safety, because the following dependencies
don't support null safety:

 - package:sim_info

For solutions, see https://dart.dev/go/unsound-null-safety

[BLIWA]

This package seems to be still not Dart 3 compatible, Is there any hope to amend for that?