[toml] Implement a TOML parser as package tomlmojo and use it to re-factor tests

[forfudan]

This pull request includes several changes to improve the testing and packaging of the decimojo and tomlmojo libraries. The most important changes involve implementing a TOML parser in package tomlmojo, restructuring the test cases to load from a TOML file, adding new test cases, and updating the packaging commands.

Improvements to testing:

• tests/biguint/test_biguint_arithmetics.mojo: Refactored the test functions (test_add, test_subtract, test_multiply, test_extreme_cases) to load test cases from a TOML file and added structured TestCase for better test management. [1] [2] [3] [4]
• src/decimojo/tests.mojo: Added a new file to implement TestCase struct and functions for managing test cases.
• tests/biguint/test_data/biguint_arithmetics.toml: Added a new TOML file to hold test data for BigUInt arithmetic operations, including addition, subtraction, multiplication, and extreme cases.

Packaging updates:

• mojoproject.toml: Updated the packaging commands to include separate packaging for decimojo and tomlmojo libraries and updated the clean command to remove additional files.

Licensing and documentation:

• src/decimojo/__init__.mojo: Removed redundant comments and updated the file header.
• src/tomlmojo/__init__.mojo: Added a new file with licensing information and initial import statements for TOML parsing.