Generalize blockwise slicing

[mtfishman]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 86.53846% with 7 lines in your changes missing coverage. Please review.

Project coverage is 77.11%. Comparing base (4ee09d2) to head (21c1476).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/BlockArraysExtensions/blockedunitrange.jl	84.37%	5 Missing ⚠️
src/abstractblocksparsearray/views.jl	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #157      +/-   ##
==========================================
+ Coverage   74.86%   77.11%   +2.24%     
==========================================
  Files          36       36              
  Lines        1973     2014      +41     
==========================================
+ Hits         1477     1553      +76     
+ Misses        496      461      -35     

Flag	Coverage Δ
docs	7.26% <0.00%> (-0.15%)	⬇️

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