Use toString(16) for num2hex and addr2hex instead of own implementation

[circl-lastname]

These two functions function the same way, but now they use toString(16), which is hopefully faster.

[marcthird128]

also u might want to use padStart(2, '0') instead of own implemntation

[circl-lastname]

I didn't know about it yet when I wrote this 4 years ago. I probably won't fix that unless the maintainer has interest in merging this patch though, I wanna see how old it can get