Change onehot to oneelement

[mtfishman]

onehot isn't quite right for the ITensor constructor that creates a tensor with a single nonzero element, see OneHotArrays.jl.

There is precedent from FillArrays.jl and Zygote.jl for calling a sparse array with a single nonzero element OneElement (https://github.com/JuliaArrays/FillArrays.jl), so here I am changing onehot to oneelement.

In the latest, this is implemented based on a new type SparseArraysBase.OneElementArray with an associated generic constructor SparseArraysBase.oneelement in a package extension, see ITensor/SparseArraysBase.jl#26.

See also #5, ITensor/SparseArraysBase.jl#24.

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 48.08%. Comparing base (e9f1be2) to head (917cf55).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/quirks.jl	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #26      +/-   ##
==========================================
+ Coverage   46.23%   48.08%   +1.85%     
==========================================
  Files           5        6       +1     
  Lines         186      183       -3     
==========================================
+ Hits           86       88       +2     
+ Misses        100       95       -5     

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[emstoudenmire]

I see what you mean. Just from the name "one hot" I would have thought things like having multiple ones and a single row or column would be forbidden (here I am referring to the example at that link). But apparently this is the usage in ML, and also one element is just a much clearer name.

[mtfishman]

I see what you mean. Just from the name "one hot" I would have thought things like having multiple ones and a single row or column would be forbidden (here I am referring to the example at that link). But apparently this is the usage in ML, and also one element is just a much clearer name.

They call that more general case a onehotbatch in OneHotArrays.jl, but still you can see the idea is to find the location of a value in a collection and use that to define a basis vector, so it is a very similar concept to how we use onehot but the application is a bit different. Anyway, I'll probably bring back onehot for backwards compatibility but deprecate it in favor of oneelement.