feat: Fix bug on `Cubic`, improvements and dependencies updates

[albertodev01]

Why?

The package needs a dependency update and some bug fixing/improvements

What?

• Added a new Factorial.computeBigInt method to calculate factorials using BigInt rather than int
• Fixed a bug in the Cubic class that throws an error when trying to solve cubic equations in the ax^3 + d = 0 form
• Updates to the Dart and Flutter example projects
• Dependencies versions update

Types of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Documentation change (change to update documentation)

Notes

In this PR I will update and rework the Flutter example application in example/flutter_example

Checklist

• [x] I have provided a description of the proposed changes.
• [x] I added unit tests for all relevant code.
• [x] In example/flutter_example, if needed, I have also added widget and golden tests.
• [ ] I added documentation for all relevant code.