Extend Closed for negative values

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Closed (n :: Nat) (m :: Nat) does not allow a closed interval that includes negative numbers due to the use of Nat. There are use cases where this would be convenient, such as representing a statistical normalized output as Closed (-1) 1.

Nat could be swapped out with a different type or alternatively an additional parameter could be added to indicate a negative offset:

type IntClosed = IntClosed Nat Nat Nat

type Closed = IntClosed Nat Nat 0