chore: revisit shuffle before persist logic

[selmanozleyen]

fixes: #194

Needs benchmarking against old code to justify refactor.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.59%. Comparing base (39a99c9) to head (db8c511).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #196      +/-   ##
==========================================
- Coverage   93.48%   91.59%   -1.89%     
==========================================
  Files          14       14              
  Lines        1121     1119       -2     
==========================================
- Hits         1048     1025      -23     
- Misses         73       94      +21     

Files with missing lines	Coverage Δ
src/annbatch/io.py	91.53% <100.00%> (+0.21%)	⬆️

... and 3 files with indirect coverage changes

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