printing of ZNElement

[borisdevos]

This is an attempt to making ZNElement printing prettier.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
src/TensorKitSectors.jl	16.66% <ø> (ø)
src/auxiliary.jl	92.64% <100.00%> (+0.22%)	⬆️
src/groupelements.jl	90.90% <100.00%> (-1.40%)	⬇️

... and 2 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[github-actions]

Your PR no longer requires formatting changes. Thank you for your contribution!

[lkdvos]

This is a bit of a personal comment but might be relevant: I find that in general the unicode symbols are quite hard to type, and actually are not that helpful in this case: \bbZ<TAB>\_2<TAB>Element is a finger workout if you compare this to Z2Element, so I'm not hugely convinced of the usefulness of this.

One thing I do see is that type_repr(::Type{ZNElement{N, p}}) where {N, p} = "GroupElement[$(type_repr(Z{N})), p]" is probably a better definition?

Just trying to follow what the goal is here, did you intend for "prettier" printing, as in more close to math output, or just shorter or more convenient?

[borisdevos]

I found for I = Z2Element{0}, the following to look fairly clunky:

julia> I(0)
GroupElement[ℤ{2}, 0](0)

julia> V = Vect[I](0 => 1, 1 => 1)
Vect[GroupElement[ℤ{2}, 0]](…) of dim 2:
 0 => 1
 1 => 1

julia> W = V^2 ← V^2
(Vect[GroupElement[ℤ{2}, 0]](0 => 1, 1 => 1) ⊗ Vect[GroupElement[ℤ{2}, 0]](0 => 1, 1 => 1)) ← (Vect[GroupElement[ℤ{2}, 0]](0 => 1, 1 => 1) ⊗ Vect[GroupElement[ℤ{2}, 0]](0 => 1, 1 => 1))

This PR would make this

julia> I(0)
ℤ₂Element{0}(0)

julia> V = Vect[I](0 => 1, 1 => 1)
Vect[ℤ₂Element{0}](…) of dim 2:
 0 => 1
 1 => 1

julia> W = V^2 ← V^2
(Vect[ℤ₂Element{0}](0 => 1, 1 => 1) ⊗ Vect[ℤ₂Element{0}](0 => 1, 1 => 1)) ← (Vect[ℤ₂Element{0}](0 => 1, 1 => 1) ⊗ Vect[ℤ₂Element{0}](0 => 1, 1 => 1))

The unicode is also just defined as aliases, as you can see here I still just type Z2Element{0}. I don't care much about how mathy it looks, so I could live with no specialised type_repr and just show Z2Element{0}, but this is somewhat consistent with how e.g. Z2Irrep and Z2Space are printed.