chore: Remove static_assertions dependency

[relrelb]

static_assertions seems unmaintained, and anyway assert!() is usable in const contexts since Rust 1.57.0:
https://blog.rust-lang.org/2021/12/02/Rust-1.57.0.html#panic-in-const-contexts So simply use the suggested method instead.

Also the rustversion dependency is no longer needed because rust-lang/rust#94075 already landed in stable.

[adrian17]

Can we keep the concrete values for the 2 platforms?

[relrelb]

Can we keep the concrete values for the 2 platforms?

Why? I thought it would be nicer to compute the sizes using current pointer size.

[adrian17]

The formula happens to check out now, but it doesn't represent a consistent underlying rule. As in:

• on 32-bit, the size upper bound comes from f64 alignment requirement (removing the Number variant would reduce the size to 12b)
• on 64-bit, the size upper bound comes from 2xpointer size plus pointer/f64 alignment (removing the String field would reduce the size to 16b).

So possible refactoring of the structs could throw the formula out of whack (plus it's reliant on what alignment our current platforms happen to have right now).

And aside from being a "regression test", having specific values at hand makes it slightly easier to eyeball memory traffic, at least for me.

[Herschel]

I agree, I prefer the explicit values in this case.

[relrelb]

Done.