Add some modifications on copula

[MooooCat]

Description

We made some updates to the copula to accommodate development calls for other composite algorithms.

Motivation and Context

The current main modifications are as follows:

• Added type hints;
• Changed the metadata settings to adapt to sdgx's Metadata and other components;
• Changed the properties of some private methods to make them accessible to other algorithms.

How has this been tested?

Types of changes

• Maintenance (no change in code, maintain the project's CI, docs, etc.)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[MooooCat]

@sjh120 Please check whether the current modifications can meet the development needs of the multi-table algorithm in sdg_ee. If not, you can continue to modify the code on this branch. You are welcome to initiate discussions at any time.

[codecov-commenter]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (1e4105d) 80.05% compared to head (a8ea428) 82.75%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
sdgx/models/statistics/single_table/copula.py	68.75%	5 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #132      +/-   ##
==========================================
+ Coverage   80.05%   82.75%   +2.69%     
==========================================
  Files          66       65       -1     
  Lines        2943     2812     -131     
==========================================
- Hits         2356     2327      -29     
+ Misses        587      485     -102     

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