Improve ProgressBar thread safety

[albertomercurio]

Description

I improved the thread safety of ProgressBar. Indeed, the previous_time variable was updated in a non-thread-safe way. I converted it into a Threads.Atomic object and then performed atomic operations on it.

Then, I also included a ReentrantLock in order to be sure that the print functions are thread-safe.

Finally, I changed the ProgressBar struct to ummutable, improving performances.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.27%. Comparing base (d469d80) to head (e7271a3).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #212      +/-   ##
==========================================
+ Coverage   93.26%   93.27%   +0.01%     
==========================================
  Files          29       29              
  Lines        2167     2172       +5     
==========================================
+ Hits         2021     2026       +5     
  Misses        146      146              

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