Copy the dataloader and trainer from yolov5

[Luwill6]

Fixing #60

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[codecov]

Codecov Report

Merging #350 (1672086) into main (d088d5f) will not change coverage.
The diff coverage is n/a.

❗ Current head 1672086 differs from pull request most recent head b06af2d. Consider uploading reports for the commit b06af2d to get more accurate results

@@           Coverage Diff           @@
##             main     #350   +/-   ##
=======================================
  Coverage   98.58%   98.58%           
=======================================
  Files          11       11           
  Lines         776      776           
=======================================
  Hits          765      765           
  Misses         11       11           

Flag	Coverage Δ
unittests	98.58% <ø> (ø)

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