Chore: Reorganize documentation and modules for vectors

[connortsui20]

Tracking Issue: #5028

Now that we have basically all of the vectors (Lists incoming later today), the crate namespace is getting super crowded. This PR removes the re-exporting into the crate level and makes all vectors accessible via the vortex-vector submodules. Additionally, this moves the main examples for each vector type into their respective modules (rather than on the mutable vector type directly).

This is a purely cosmetic change that makes it easier to navigate the documentation of vortex-vector. Given that this is effectively going to be Vortex's IR, I think it is important to be more careful about what we put into the top-level namespace.

If people don't like having to type out an extra word when importing, then I would suggest we add a prelude rather than forcing everything at the top level.

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.05%. Comparing base (784bad9) to head (ffef105).
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[gatesn]

I don't know why we would change the namespacing? Yeah there's a bunch of things, but it's finite and as you say, complete.

[connortsui20]

It's very difficult to understand what to look for when on the "landing" page docs. This way, it is obvious what is what (for example Vector is the top-level type and everything else is a variant of it, if you have 20+ types all in the same place there is no chance you will understand that)