Resolve #479

[bwohlberg]

Resolve #479.

The solution is to simply remove the VerticalStack-specific arithmetic operator definitions, the need for which is unclear.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (5c83511) 94.83% compared to head (7afe23b) 94.76%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #480      +/-   ##
==========================================
- Coverage   94.83%   94.76%   -0.08%     
==========================================
  Files          91       91              
  Lines        5651     5626      -25     
==========================================
- Hits         5359     5331      -28     
- Misses        292      295       +3     

Flag	Coverage Δ
unittests	94.76% <100.00%> (-0.08%)	⬇️

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[Michael-T-McCann]

With this PR, we lose the ability to add two VerticalStacks together and get another VerticalStack rather than a generic Operator or LinearOperator. I am willing to give that up to reduce code duplication. There may be other places in the code with a similar pattern.

[bwohlberg]

With this PR, we lose the ability to add two VerticalStacks together and get another VerticalStack rather than a generic Operator or LinearOperator. I am willing to give that up to reduce code duplication. There may be other places in the code with a similar pattern.

This was intentional. It isn't clear what real benefit there is to this capability, and it requires considerable additional complexity. It seems simplest to remove it for now, and re-enable it if we discover some significant use for it.