Added copy constructor and test case for min heap

[Xoulios]

I think the add copy constructors to all classes issue can be closed now

[spirosmaggioros]

I think there's a library missing for INT_MAX/INT_MIN cause the build is failing.
Good thing that we have automatic test running now, in every push to this branch test cases will run automatically and have to pass. I think it's a minor error, you can see in the build process what failed in details(Basically add the climits library)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.50%. Comparing base (1a9f1af) to head (dba6522).
Report is 13 commits behind head on main.

❗ Current head dba6522 differs from pull request most recent head 3f042df. Consider uploading reports for the commit 3f042df to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #47      +/-   ##
==========================================
- Coverage   97.69%   97.50%   -0.19%     
==========================================
  Files          85       91       +6     
  Lines        3036     3249     +213     
  Branches      494      526      +32     
==========================================
+ Hits         2966     3168     +202     
- Misses         70       81      +11     

Files	Coverage Δ
src/classes/heap/min_heap.h	86.84% <100.00%> (ø)
tests/heap/min_heap.cc	100.00% <100.00%> (ø)

... and 4 files with indirect coverage changes

[Xoulios]

I do not know what keeps failing. Everything seems to be alright on my machine.

[spirosmaggioros]

Can you add some if statements and maybe some more checks for the code?
It seems that the coverage dropped 0.12%, so see if you can do something about it otherwise i will look at it