Number.slice and .static_array use unsafe casting

[straight-shoota]

Number.slice and Number.static_array use Number.new! to cast values to the item type which does not fail on overflow errors:

Int8.slice(0x1234, 1023.0) # => Slice[52, -1]

This is unsafe behaviour and should be fixed.
The easiest fix would be to change Number.new! to Number.new. This would have a minor performance impact, but that shouldn't be too much of a problem (and safety is definitely more important).
Common usage of these macros is with number literals for which we could easily use implicit autocasting.

First reported in #13020 (comment)