Concrete improvements:
 * Added safety for integer overflow (-MAX_INT/-1)
 * Omit division by zero safety check when RHS is comptime known to
   be non-zero.
 * Avoid emitting `_optimized` variants of AIR instructions for integers
   (this suffix is intended to be used for floats only).

Subjective changes: I extracted the div logic out from analyzeArithmetic
in order to reduce the amount of branches - not for performance reasons
but for code clarity. It is more lines of code however, and some logic
is duplicated.