change assert to evaluate at comptime for approxEqRel

[pollend]

This assert can be evaluated at comptime.

[triallax]

i'm pretty sure the assert gets evaluated at comptime regardless

[nektro]

prior to this patch it'd be a runtime panic instead of a compile error.

[pollend]

this compiles in compiler explorer this should be a compile time error: https://godbolt.org/z/PW6zjz551

[triallax]

prior to this patch it'd be a runtime panic instead of a compile error.

huh, i even checked the generated assembly but i suppose it didn't show any problems because i was using f64 rather than an invalid type, that's my bad