Improvements using const generics

[bluss]

There are a few minor features and improvements we can do with const generics. This meta-issue is mainly about those.

Big-ticket items get their own issue. In particular remaking index and dimension types gets is own ticket.

Easy add-ons

• IntoNdProducer impl for &[T; N]
• FixedInitializer or replacement impl for &array - replace with just const generics of arrays
• From<&array> and similar implementations
• NdIndex / Index impls using [T; N] in particular for ixdyn ?

Long term features

• Overhaul of dimension types. See separate issue: Plan for dimension types #519
• Dimension/pattern/index types using arrays for pattern matching

[JulianKnodt]

I was looking at the codebase, and was wondering if there was anything more to implement for const generics? I browsed through the linked issue for dimension types, but it seems older and likely has significantly changed since then. There was also a recent issue about converting dimensions to const generics, and was wondering how viable that was/what is missing from const generics for that to happen?