Fix CI Issues

[posborne]

From #290 there were some CI failures unrelated to that change; attempting to fix and simplify things a little bit.

• Drop nightly toolchain -- I'm not aware of a reason that is required at this point.
• Pin libsodium to the single tagged release that exists rather than chasing stable (which had broken when using zig 0.12).
• Bump the wasmtime REVISION; v25 and the older commit no longer compile with stable it appeared.

I'll add commits if CI fails with additional bits to address.

[posborne]

The windows failure has to do with dropping nightly and some antiquated code paths in the precision crate that, I believe, are assuming that inline assembly for rust isn't available on stable. Since that has been available for some time, I'll probably look to patch (and upstream) changes to precision as the path forward on that.

[posborne]

The most recent commit should not have fixed anything, but it appears that it did or the windows failure is spurious :/

I'm willing to call this ready for review unless others have specific suggestions on Windows -- I don't currently have ready access to a Windows machine to diagnose Windows specific failures.

[posborne]

jedisct1/rust-precision#13 has the upstreaming request for the precision crate. I'm still not sure why the linking issue on windows with the C version arose, but making the suggested change there seemed worthwhile and easier than debugging the linker issue.

[posborne]

r? @abrown or @fitzgen

[posborne]

It looks like this update also ends up incorporating the changed proposed in #241 but with a fix for the precision/windows issues.