Latest nightly fix

[BGluth]

There's one compiler error that's preventing us from building on the latest nightly, and I managed to resolve it by making a paremeter into a reference. I tried a few other things before resorting to using a reference (like #![feature(const_precise_live_drops)]), but I couldn't get it to compile. I think using a reference here should have no performance changes (since it's still a const fn at the end of the day), but let me know if there's a better way to fix this error.

For reference, the error was this:

error[E0493]: destructor of `[std::ops::RangeInclusive<u8>; N]` cannot be evaluated at compile-time
  --> evm/src/cpu/kernel/constants/exc_bitfields.rs:7:53
   |
7  | const fn u256_from_set_index_ranges<const N: usize>(ranges: [RangeInclusive<u8>; N]) -> U256 {
   |                                                     ^^^^^^ the destructor for this type cannot be evaluated in constant functions
...
29 | }
   | - value is dropped here

Resolves #1186.

[BGluth]

I don't know if we want to do this, but we could also update the CI to use the latest nightly (or keep it on 2023-06-30 if we want something that we know will keep working). There's also #1195, which if we want we might as well merge and update it to point to a more up to date nightly.

[npwardberkeley]

That sounds good to me!! It'd be nice to be on the latest version everywhere, including in the CI. Regarding #1195, can we set the rust-toolchain to just nightly? Or does it always need to be a particular one that we'd need to keep updating?

[BGluth]

We can definitely just have it point to the latest nightly. It just might mean that CI will randomly fail (which maybe is a good thing anyways) and we'll have to fix it.