BREAKING CHANGE: Replace symmetry type with enum

[IvanaGyro]

Changes

• Replaced class SymmetryType_class with enum SymmetryType
• Removed struct __sym (I mention here because C++ doesn't have name mangling like Python. Removing this structure indeed breaks the interface.)
• Removed singleton instance SymType

Following Steps

I am going to remove the dependency of boost in the Symmetry class. There are two options:

1. Merged class U1Symmetry and class ZnSymmetry into class Symmetry and used switch-like syntax to delegate the member functions
2. Used std::variant to directly hold the instance of class U1Symmetry and class ZnSymmetry in Symmetry.

[codecov[bot]]

Codecov Report

:x: Patch coverage is 33.33333% with 12 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 22.17%. Comparing base (31da063) to head (dec3770). :warning: Report is 42 commits behind head on master.

Files with missing lines	Patch %	Lines
include/Symmetry.hpp	37.50%	7 Missing and 3 partials :warning:
src/Symmetry.cpp	0.00%	2 Missing :warning:

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #586   +/-   ##
=======================================
  Coverage   22.17%   22.17%           
=======================================
  Files         211      211           
  Lines       51053    51044    -9     
  Branches    19010    19006    -4     
=======================================
  Hits        11319    11319           
+ Misses      37969    37960    -9     
  Partials     1765     1765           

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[hunghaoti]

I believe the original design intention was to allow for easy switching between Python and C++. For instance, if the Python code uses SymType.U, the C++ code would also use SymType.U.

If we change SymType to an enum , the syntax in C++ would become SymType::U. In my point of view it is acceptable. Since we have similar issue when using namespace in C++. For example, in Python we write cytnx.random.uniform(...), and in C++ we write cytnx::random::uniform(...). @kaihsin , what do you think about it?

If we decide to use enum, we can consider using enum class.

[ianmccul]

eventually you will want to make this something more general, so that you can add new symmetries later, ideally as an extension that doesn't require modifying existing code.

[kaihsin]

I agree with @ianmccul . For now, yes. Let's do enum

[hunghaoti]

I suggest that in the future we can consider replacing enum with enum class.

[yingjerkao]

Is this PR good to merge?

[hunghaoti]

I agree this PR is good to merge. @IvanaGyro , what do you think?

[IvanaGyro]

I thought to merge this PR after changing SymType to SymmetryType and mark SymType deprecated. This job was pending because I set updating build process and supporting Mac at higher priority.

We can merge this PR now and add the new Python API in the future.