Using Const<4> instead of Const<{ U4::USIZE }> is better for rust-analyzer

[digama0]

From rust-lang/rust-analyzer#11803 (comment) :

There is literaly no const eval in const generics yet, so Const<{ four }> is Const<_>. We can handle this special case easily, but the constants in nalgebra are very complex and evaluating them needs trait resolution (#4558) + lowering const generics to body (#7434) + evaluating assoc consts with generic parameters. Short term solution here IMO is replace type u4 = Const<{ typenum::U4::USIZE }> with type U4 = Const<4> in the nalgebra source code, which is an internal and invisible to user change.

Would this be a reasonable change to make? Rust analyzer has a lot of trouble with nalgebra's types, and this is a big impediment to using the crate in beginner settings. Arguably this is a problem that rust analyzer should solve, but if a simple fix like this helps it seems worthwhile.

[sebcrozet]

Hi! Yes, this can easily be done. I agree we should make the change if it makes it easier for rust-analyzer.