Add progress bars to backtest.py

[nathanramoscfa]

What's Changed

• Modified backtest.py to display a progress bar during calculations.

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (2581278) 45.47% compared to head (38767ce) 45.50%.
Report is 2 commits behind head on master.

Files	Patch %	Lines
bt/backtest.py	66.66%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #423      +/-   ##
==========================================
+ Coverage   45.47%   45.50%   +0.02%     
==========================================
  Files           4        4              
  Lines        1935     1936       +1     
  Branches      449      449              
==========================================
+ Hits          880      881       +1     
  Misses        998      998              
  Partials       57       57              

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