feat: Approximate pi with machin's formula

[56ghluf]

Description of Change

Checklist

• Added description of change
• Added file name matches File name guidelines
• Added tests and example, test must pass
• Added documentation so that the program is self-explanatory and educational - Doxygen guidelines
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Notes:
Added a file math/pi_machin.cpp. Creates a namespace in the math namespace called pi_approximation. Includes a function in this namespace which approximates pi by using Machin's formula and the power series of arctan (see https://en.wikipedia.org/wiki/Machin-like_formula).