Add checked operations for integer based newtypes

[Kamil729]

This PR implements checked arithmetic operations for newtypes whose inner types are integers. It adds an attribute, similar to new_unchecked that enable this.

I considered implementing this as a num_traits derives, but those require regular operators to be implemented for those types, so I wanted some feedback on this.

I was also thinking about implementing wrapping and saturating variants, but again I would like to get some feedback on this beforehand.