Fix generic show for block sparse arrays

[mtfishman]

Fixes #63, using the same code pattern that was used in ITensor/NamedDimsArrays.jl#48.

The show methods also have to be updated to reflect the changes @lkdvos made in ITensor/SparseArraysBase.jl#31, but this is orthogonal to that issue since this PR is only about how the types are printed, not how the unstored values are printed.

[codecov]

Codecov Report

Attention: Patch coverage is 89.65517% with 3 lines in your changes missing coverage. Please review.

Project coverage is 74.59%. Comparing base (bfe3820) to head (f5c626d).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...stractblocksparsearray/abstractblocksparsearray.jl	89.65%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #65      +/-   ##
==========================================
- Coverage   75.49%   74.59%   -0.91%     
==========================================
  Files          29       29              
  Lines        1106     1106              
==========================================
- Hits          835      825      -10     
- Misses        271      281      +10     

Flag	Coverage Δ
docs	24.88% <0.00%> (ø)

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[lkdvos]

Do you want me to add that change to this PR as well?

[mtfishman]

Do you want me to add that change to this PR as well?

I'll merge this and we can do that in a followup PR, I think that would require other updates for SparseArraysBase.jl v0.3 anyway.