reshape(::OneToOne)

[ogauthe]

This PR allows Base.reshape to handle OneToOne similarly to Base.OneTo(1), to be used e.g. in TensorAlgebra.fusedims.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (fc0668a) to head (154849e).
Report is 1 commits behind head on main.

Additional details and impacted files

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  Files            4         4           
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+ Hits            20        21    +1     

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[ogauthe]

In TensorAlgebra I end up using to_shape.(axes), so I can solve the current issue just by defining Base.to_shape(::OneToOne) = 1. This avoids type piracy and allows natural code to work.

[ogauthe]

Since we ended up not using OneToOne in ITensor/TensorAlgebra.jl#50, we may decide to completely remove it. If we prefer to keep it I think we can merge this PR that just defines Base.to_shape(::OneToOne)

[mtfishman]

I'll merge this, but let's keep an eye out for uses of OneToOne that we can remove.