file extensions in Save() and Load() methods are optional

[manuschneider]

Fixes #727.

If no file extension is given, the standard extension for the corresponding object type is added to the filename.

This is backwards compatible with the previous behavior but allows to use custom file extensions and call Save() and Load() with the exact same arguments.

[codecov]

Codecov Report

❌ Patch coverage is 8.69565% with 42 lines in your changes missing coverage. Please review.
✅ Project coverage is 35.47%. Comparing base (fa015d4) to head (42e86b1).
⚠️ Report is 19 commits behind head on master.

Files with missing lines	Patch %	Lines
src/backend/Storage.cpp	0.00%	10 Missing ⚠️
src/Symmetry.cpp	0.00%	8 Missing ⚠️
src/Tensor.cpp	12.50%	7 Missing ⚠️
src/tn_algo/MPS.cpp	0.00%	7 Missing ⚠️
src/Bond.cpp	0.00%	6 Missing ⚠️
src/UniTensor.cpp	42.85%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #728      +/-   ##
==========================================
+ Coverage   35.44%   35.47%   +0.02%     
==========================================
  Files         215      214       -1     
  Lines       33071    33007      -64     
  Branches    13170    13130      -40     
==========================================
- Hits        11723    11709      -14     
+ Misses      19424    19376      -48     
+ Partials     1924     1922       -2     

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[IvanaGyro]

I suggest deprecate the feature that automatically adds file extension while saving and keep the function for loading unchanged. Automatically appending file extension while saving and loading files is uncommon practice.

Additionally, can you squash the two commits in this PR?

[manuschneider]

I suggest deprecate the feature that automatically adds file extension while saving and keep the function for loading unchanged. Automatically appending file extension while saving and loading files is uncommon practice.

I thought it might actually be handy to just provide the base name and cytnx will add the common extension for this type of object. We can have a separate issue on deprecating this, but this might affect basically all unit tests.

Additionally, can you squash the two commits in this PR?

How do I best squash them with git?

[IvanaGyro]

How do I best squash them with git?

Using git rebase -i is the most intuitive way. See: https://stackoverflow.com/a/5189600