Replace some problematic uses of String::num to String::num_int64

[adamscott]

This PR replaces some problematic uses of String::num to String::num_int64. I made sure to check that the source variable is indeed an int.

This is a regression from #47502
Fixes #101553

[adamscott]

cc. @KoBeWi

[Ivorforce]

Great find!
Did you go through all String::num callers to make sure there are no other regressions? It may be possible to statically find other incompatible ones by temporarily re-defining the function as static String num(std::enable_if_t<std::is_floating_point_v<double>, double> p_num, int p_decimals = -1);, and simply recompiling.

[akien-mga]

Thanks!

[KoBeWi]

I wonder why we don't have some universal number to string method.
Although instead of concatenating and being careful about types, these strings should just use vformat().