There's a bug in Slice indexing where it returns a value when there should be an exception

[BrucePay]

The following code tests a buggy behaviour when indexing slices. The .Index code will allow you to index 1(?) past the formal length of the slice when there should have been an error. This is easy to fix but it causes a bunch of the internal uses of ^Slice to break. It all needs to be fixed and the slice code needs to be simplified/clarified.

(test/exec :slice36
    (\ ->
        (let s (slice [1 2 3 4] 1 -1))
        [ (!! s 0) (!! s 1) (!! s 2) ]  ; indexing 2 here should throw an exception
    )
    [2 3 4]
)

[BrucePay]

Hmmm ... this is more complicated. Indexing seems to be limited by the physical buffer rather than the logical buffer as shown in the following:

(let s (slice [1 2 3 4 5] 1 -2)) 
(!! s 0)  ; works and should work
(!! s 1)  ; works and should work
(!! s 2)  ; works but shouldn't work
(!! s 3)  ; works but shouldn't work
(!! s 4)  ; correctly throws exception