fix buffered dataloader

[CarloLucibello]

fix #205

Also adds small improvements to printing

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 12.50000% with 7 lines in your changes missing coverage. Please review.

Project coverage is 81.40%. Comparing base (4067267) to head (0f183f8).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/dataloader.jl	12.50%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #206      +/-   ##
==========================================
- Coverage   84.93%   81.40%   -3.53%     
==========================================
  Files          15       15              
  Lines         697      667      -30     
==========================================
- Hits          592      543      -49     
- Misses        105      124      +19     

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