Bump curve25519-dalek to latest

[salman01zp]

Bump curve25519-dalek to fix nighlty build Issue

https://github.com/dalek-cryptography/curve25519-dalek/pull/619

 error[E0658]: use of unstable library feature 'stdsimd'
  --> /home/runner/.cargo/registry/src/index.crates.io-6f17d22bba15001f/curve25519-dalek-4.1.2/src/backend/vector/ifma/field.rs:26:5
   |
26 |     _mm256_madd52lo_epu64(z.into(), x.into(), y.into()).into()
   |     ^^^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #48556 <https://github.com/rust-lang/rust/issues/48556> for more information
   = help: add `#![feature(stdsimd)]` to the crate attributes to enable

error[E0658]: use of unstable library feature 'stdsimd'
  --> /home/runner/.cargo/registry/src/index.crates.io-6f17d22bba15001f/curve25519-dalek-4.1.2/src/backend/vector/ifma/field.rs:25:9
   |
25 |     use core::arch::x86_64::_mm256_madd52lo_epu64;
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #48556 <https://github.com/rust-lang/rust/issues/48556> for more information
   = help: add `#![feature(stdsimd)]` to the crate attributes to enable

error[E0658]: use of unstable library feature 'stdsimd'
  --> /home/runner/.cargo/registry/src/index.crates.io-6f17d22bba15001f/curve25519-dalek-4.1.2/src/backend/vector/ifma/field.rs:34:5
   |
34 |     _mm256_madd52hi_epu64(z.into(), x.into(), y.into()).into()
   |     ^^^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #48556 <https://github.com/rust-lang/rust/issues/48556> for more information
   = help: add `#![feature(stdsimd)]` to the crate attributes to enable

error[E0658]: use of unstable library feature 'stdsimd'
  --> /home/runner/.cargo/registry/src/index.crates.io-6f17d22bba15001f/curve25519-dalek-4.1.2/src/backend/vector/ifma/field.rs:33:9
   |
33 |     use core::arch::x86_64::_mm256_madd52hi_epu64;
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #48556 <https://github.com/rust-lang/rust/issues/48556> for more information
   = help: add `#![feature(stdsimd)]` to the crate attributes to enable

error[E0635]: unknown feature `stdarch_x86_avx512`
  --> /home/runner/.cargo/registry/src/index.crates.io-6f17d22bba15001f/curve25519-dalek-4.1.2/src/lib.rs:19:13
   |
19 |     feature(stdarch_x86_avx512)
   |             ^^^^^^^^^^^^^^^^^^

[burdges]

I'd still meant to look at this one, but there was enough churn in dalek that I wanted ot be careful.

[salman01zp]

We switched to stable rust to fix this issue. So no rush with updates