Correctly specify nullability of Subject for NumericAssertions

[vbreuss]

Background and motivation

The Subject of NumericAssertions is always not-null, but because NullableNumericAssertions inherits from it, the subject was specified as nullable. This causes a lot of warnings (e.g. "Possible 'System.InvalidOperationException'").

I suggest to add a new base class NumericAssertionsBase which also gets the type of the subject and thus the NullableNumericAssertions now has a nullable subject and the subject of NumericAssertions is not-null.

Alternative Concerns

No response

Are you willing help with a pull-request?

Yes, please assign this issue to me.

[vbreuss]

I created a draft-PR to clarify, what my suggestion looks like.

[dennisdoomen]

That draft PR seems to be using a ! a lot. How does it really improve the situation?

[vbreuss]

That draft PR seems to be using a ! a lot. How does it really improve the situation?

Sorry, I forgot to remove some unrelated changes. I updated the PR #2473 accordingly.