Added an algorithm to calculate the present value of cash flows (#8700)

* Added an algorithm to calculate the present value of cash flows

* added doctest and reference

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* Resolving deprecation issues with typing module

* Fixing argument type checks and adding doctest case

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* Fixing failing doctest case by requiring less precision due to floating point inprecision

* Updating return type

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* Added test cases for more coverage

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* Make improvements based on Rohan's suggestions

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* Update financial/present_value.py

Committed first suggestion

Co-authored-by: Christian Clauss <cclauss@me.com>

* Update financial/present_value.py

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Co-authored-by: Christian Clauss <cclauss@me.com>

* Update financial/present_value.py

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Co-authored-by: Christian Clauss <cclauss@me.com>

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Christian Clauss <cclauss@me.com>