Optimize NULL handling for `lcm`, `gcd`

[neilconway]

Is your feature request related to a problem or challenge?

These functions check for and build NULLs iteratively; faster to use Arrow kernels like try_unary or try_binary, which compute the result NULL buffer more efficiently via bitwise union.

Describe the solution you'd like

No response

Describe alternatives you've considered

No response

Additional context

No response

[neilconway]

take