merge BlockIndexRange using BlockArrays

[ogauthe]

adapt to JuliaArrays/BlockArrays.jl#470

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.47%. Comparing base (c8f3ad5) to head (61d6822).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #63      +/-   ##
==========================================
- Coverage   91.52%   91.47%   -0.05%     
==========================================
  Files          11       11              
  Lines         578      575       -3     
==========================================
- Hits          529      526       -3     
  Misses         49       49              

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

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