Bump MSRV to 1.73

[StackOverflowExcept1on]

Motivation:

1. We can get rid of lazy_static! in favor of std::sync::LazyLock
2. We can use {integer}::div_ceil
   

   frost/frost-core/src/scalar_mul.rs

   Line 28 in ca33dad

   const fn div_ceil(lhs: usize, rhs: usize) -> usize {

3. Crates from RustCrypto already have pre-releases that require Rust 1.73+ or even Rust 1.81+ in some cases. For example: https://github.com/RustCrypto/elliptic-curves/blob/master/k256/Cargo.toml
4. Starting with 1.81 we can use core::error::Error and remove the thiserror-nostd-notrait dependency in favor of thiserror: Allow disabling std dependency on 1.81+ dtolnay/thiserror#373

[conradoplg]

This is REALLY tempting, but we might want to give a bit more time to crate users to update their Rust. I'm leaving this open while we consider it. Thanks for pointing these out!

[str4d]

Providing the full context:

• LazyLock requires MSRV 1.80, but OnceLock could also be used to get rid of lazy_static!, and it only requires MSRV 1.70.
• {integer}::div_ceil requires MSRV 1.73.
• RustCrypto had an MSRV of 1.73 as their last common MSRV IIRC (the latest non-pre-release of k256 is actually MSRV 1.65), but have bumped to 1.81 in pre-releases of crates that were using generic-array to instead use hybrid-array, which has an MSRV of 1.81 simply to remove its std feature flag and replace std::error::Error with core::error::Error: Remove std RustCrypto/hybrid-array#85
  • Based on Remove std RustCrypto/hybrid-array#85 (comment) I believe they plan to hold off actually cutting releases of those downstream crates (such as the aforementioned k256) until 1.81 is at N - 3 (i.e. waiting until the release of Rust 1.84 in early 2025). And I do not think that the FROST crates should depend on pre-releases of those crates.

[conradoplg]

Thanks - I guess we better wait until 1.84 at least.

It seems sensible to follow RustCrypto MSRV so we might already do the first two.

[mpguerra]

We've decided to update to 1.73 for now