docs: Update and extension of Javadocs for entities

[o-kopysov]

Pull Request

Description

This PR extends Javadocs for all entity classes and enums.
Related to #307.
Also, refactored source code where needed.

Type of change

Please delete options that are not relevant.

• 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)
• Code cleanup/refactoring
• Documentation update
• This change requires a documentation update
• CI system update
• Test Coverage update

Checklist:

• My code follows the style guidelines of this project
• My code meets the required code coverage for lines (90% and above)
• My code meets the required code coverage for branches (80% and above)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6600bd2) 91.36% compared to head (8fab7f7) 91.34%.

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #355      +/-   ##
============================================
- Coverage     91.36%   91.34%   -0.02%     
+ Complexity      478      475       -3     
============================================
  Files            49       48       -1     
  Lines          1609     1606       -3     
  Branches        194      194              
============================================
- Hits           1470     1467       -3     
  Misses           82       82              
  Partials         57       57              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[o-konoval]

Great job! Approved!