chore: fix winterfell deprecations and no-std build setup

[bitwalker]

This change addresses upstream deprecations/changes from facebook/winterfell#262 and 0xPolygonMiden/crypto#290.

As a necessary side effect of those deprecations, our no-std build setup needed to be adjusted. See the above-mentioned PRs for more info, but the gist of the change is to always build with #![no_std], and enable std features conditionally, rather than the reverse. For the most part this has little effect on how code is actually written, aside from needing to be more explicit about imports in some cases (anything that would normally be provided by the libstd prelude).

[hackaugusto]

There seems to be one standing warning and some rustfmt changes:

2024-03-21T18:06:15.0030965Z error: the item `Box` is imported redundantly
2024-03-21T18:06:15.0089521Z ##[error] --> mock/src/main.rs:1:11
2024-03-21T18:06:15.0161020Z   |
2024-03-21T18:06:15.0162741Z 1 | use std::{boxed::Box, fs::File, io::Write, path::PathBuf, time::Instant};
2024-03-21T18:06:15.0164185Z   |           ^^^^^^^^^^
2024-03-21T18:06:15.0165886Z  --> /rustc/1388d7a069d872bcfe5e5dd97ef61fa0a586fac0/library/std/src/prelude/mod.rs:125:13
2024-03-21T18:06:15.0167515Z   |
2024-03-21T18:06:15.0169363Z   = note: the item `Box` is already defined here
2024-03-21T18:06:15.0170161Z   |
2024-03-21T18:06:15.0171029Z   = note: `-D unused-imports` implied by `-D warnings`

[hackaugusto]

Thanks!!

[bitwalker]

@hackaugusto I've gotta remember to re-run all my checks with both stable and nightly toolchains, that's why I missed those items, sorry about that!

Everything is green now, so I've gone ahead and merged, but let me know if anything else comes up related to those changes.

[Dominik1999]

Can you do the same for main @bitwalker ?

[bobbinth]

@Dominik1999 Once we merge next into main these will go away. Is there any reason to do it sooner?

[Dominik1999]

@bobbinth yes, the question is if we need to fix this before we merge docs PRs. PRs that touch the docs would go to main. And we can merge with the clippy warning, but that might be bad practice.

[bobbinth]

I think if it affecting only docs, clippy warnings are ok.