feat: add ClassDeclStmt and ClassDefStmt

[apkrelling]

Pull Request description

This PR adds ClassDeclStmt and ClassDefStmt classes.
This PR is an attempt to resolve #90 .

• added new ASTKind's
• created ClassDeclStmt class
• created ClassDefStmt class
• updated __init__.py to include the new imports and classes in the __all__ list
• added test for ClassDeclStmt class
• added test for ClassDefStmt class
• added transpiler visit method for ClassDeclStmt
• added transpiler test for ClassDeclStmt
• added transpiler visit method for ClassDefStmt
• added transpiler tests for ClassDefStmt

How to test these changes

Pull Request checklists

This PR is a:

• bug-fix
• new feature
• maintenance

About this PR:

• it includes tests.
• the tests are executed on CI.
• the tests generate log file(s) (path).
• pre-commit hooks were executed locally.
• this PR requires a project documentation update.

Author's checklist:

• I have reviewed the changes and it contains no misspelling.
• The code is well commented, especially in the parts that contain more
  complexity.
• New and old tests passed locally.

Additional information

Reviewer's checklist

Copy and paste this template for your review's note:

## Reviewer's Checklist

- [ ] I managed to reproduce the problem locally from the `main` branch
- [ ] I managed to test the new changes locally
- [ ] I confirm that the issues mentioned were fixed/resolved .