Remove usage of GradedUnitRanges

[mtfishman]

This is a step towards making BlockSparseArrays.jl a dependency of GradedArrays.jl.

[codecov]

Codecov Report

Attention: Patch coverage is 63.15789% with 21 lines in your changes missing coverage. Please review.

Project coverage is 73.31%. Comparing base (24d8cec) to head (a7ea884).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/BlockArraysExtensions/blockedunitrange.jl	63.15%	21 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #93      +/-   ##
==========================================
- Coverage   76.37%   73.31%   -3.06%     
==========================================
  Files          28       27       -1     
  Lines        1075     1068       -7     
==========================================
- Hits          821      783      -38     
- Misses        254      285      +31     

Flag	Coverage Δ
docs	16.44% <0.00%> (+0.09%)	⬆️

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