Use Summed from MapBroadcast.jl

[mtfishman]

Use Summed from MapBroadcast.jl introduced in ITensor/MapBroadcast.jl#17 to simplify the broadcasting implementation.

[codecov]

Codecov Report

❌ Patch coverage is 94.44444% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 75.68%. Comparing base (0f2daf7) to head (88e9fbd).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/fillarrays/kroneckerarray.jl	90.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #37      +/-   ##
==========================================
- Coverage   79.63%   75.68%   -3.95%     
==========================================
  Files          13       13              
  Lines         874      872       -2     
==========================================
- Hits          696      660      -36     
- Misses        178      212      +34     

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

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