feat: add Pi spigot algorithm

[alexdev8930]

Description of Change

Adds a Rabinowitz-Wagon spigot algorithm that generates 42 decimal digits of Pi using integer arithmetic without floating-point calculations.

The program includes comments explaining the algorithm and self-tests for the output format and first digits of Pi.

References

None.

Checklist

• Added description of change
• Added file name matches the file name guidelines
• Added tests and example, test must pass
• Relevant documentation/comments is changed or added
• PR title follows semantic commit guidelines
• Searched previous suggestions before making a new one
• I acknowledge that all my contributions will be made under the project's license.