refactor: change sequence statement to more functional approach

[marcelomamorim]

Pull Request: Functional Refactoring and Enhanced Testing

Summary

This pull request refines the Sequence statement execution logic with a more functional approach and introduces additional tests to strengthen the interpreter's evaluation and execution functions.

Changes Made

1. Refactored Sequence Execution Logic:

   • Simplified the Sequence statement execution by leveraging and_then, improving readability and making error handling more concise.
   • New Sequence logic:

     Statement::Sequence(s1, s2) => {
         execute(s1, env).and_then(|new_env| execute(s2, new_env))
     }

2. Added Tests for Core Functionality:

   • Expanded test coverage to include more complex scenarios, such as nested expressions, conditionals, and loops.
   • New tests confirm variable assignments, loop operations, and conditional branching functionality, ensuring the interpreter’s robustness.

Additional Notes

• The refactor moves the code toward a more functional style by chaining operations and reducing nested structures.
• This update maintains all previously defined behaviors with no breaking changes.

[helpmehelpus]

Looks good! Just give cargo fmt a run. We can - and probably should - automate this eventually

[marcelomamorim]

Looks good! Just give cargo fmt a run. We can - and probably should - automate this eventually

Done :)