Improve (arg-)max/minimum

[kchanqvq]

Thanks for being so responsive! These are the commits split from my last PR, as requested :)

[digikar99]

Other than the two minor points, the other addition this PR requires would be analogous changes to the src/basic-math/* files for numericals.

[kchanqvq]

I synchronized the changes to numericals/src. I changed return type of arg-* to (signed-byte 64) but that seems to hit a peltadot error. About <type> in return type, I didn't find it to cause any issue so far (not sure if it propagates correctly, but that's supposedly peltadot's responsibility as well).

[digikar99]

About in return type

Just rechecked. Type parameters like <type> in a pflet inside the body of a polymorph or in the return type of a polymorph pose no problems as long as there is a preceding <type> parameter as part of a orthogonally specializing type in the type list of the polymorph. If there's no <type> as part of a orthogonally specializing type in the type list of the polymorph or if it's a stray <type>, then that can pose a problem.