Disabled debugchk for array get

[onehundredfeet]

Currently, the code is debug checking every array access for non basic types. Most of the other calls in the code to unsafe_cast_to use '~debugchk:false` but array access did not. This was a big hit for tight loops where a check on casting was evaluated in production code.

[ncannasse]

This is not so easy. I think I kept it because there's several cases where the type needs to be cast, especially when dealing with interfaces, structures, or polymorphic arrays.

[onehundredfeet]

The cast is still there, it's just the debug check that's disabled. Unless, I'm misunderstanding what the flag does.

The debug check seems to just assert when the cast fails. I'd love to hook this up to a compiler flag but it's beyond my ocml atm.