[WIP] Improve slicing to help GradedArrays [un]matricize

[mtfishman]

These are some fixes that help with implementing [un]matricize for GradedArrays, see ITensor/GradedArrays.jl#129.

[codecov]

Codecov Report

❌ Patch coverage is 70.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.51%. Comparing base (3cf1b66) to head (79ebb14).

Files with missing lines	Patch %	Lines
...sorAlgebraExt/BlockSparseArraysTensorAlgebraExt.jl	42.85%	4 Missing ⚠️
src/abstractblocksparsearray/arraylayouts.jl	83.33%	2 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (3cf1b66) and HEAD (79ebb14). Click for more details.

HEAD has 5 uploads less than BASE

Flag	BASE (3cf1b66)	HEAD (79ebb14)
	6	1

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #247      +/-   ##
==========================================
- Coverage   71.94%   64.51%   -7.43%     
==========================================
  Files          36       35       -1     
  Lines        2032     2018      -14     
==========================================
- Hits         1462     1302     -160     
- Misses        570      716     +146     

Flag	Coverage Δ
docs	5.79% <0.00%> (-0.04%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.