Soundness with panicking drop

[bluss]

Just for reference, I believe literator runs into the same issue that ArrayVec has seen during its development:

Panic in element's drop leads to double dropping, issue https://github.com/bluss/arrayvec/issues/3

The summary is that the drop inhibition (writing None) is not reached, and then the whole array drops during unwinding. This is a edge case scenario and I guess it might change depending on MIR (just throwing in a disclaimer)?.

ArrayVec solved this by splitting the element drop and the drop inhibition into two different types (ArrayVec vs NoDrop), so that the latter always runs even if the first panics.