Create Days Sales Outstanding in Financial

[Curts0]

Describe your change:

• [X] Add an algorithm?
• [ ] Fix a bug or typo in an existing algorithm?
• [ ] Documentation change?

Checklist:

• [X] I have read CONTRIBUTING.md.
• [X] This pull request is all my own work -- I have not plagiarized.
• [X] I know that pull requests will not be merged if they fail the automated tests.
• [X] This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• [X] All new Python files are placed inside an existing directory.
• [X] All filenames are in all lowercase characters with no spaces or dashes.
• [X] All functions and variable names follow Python naming conventions.
• [X] All function parameters and return values are annotated with Python type hints.
• [X] All functions have doctests that pass the automated testing.
• [X] All new algorithms have a URL in its comments that points to Wikipedia or other similar explanation.
• [x] If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[Curts0]

ran flake8, mypy, black, & doctest locally without issue. First time contributing to this repo, read through CONTRIBUTING.md I believe I followed all steps

[cclauss]

Is DSO this? If not, why force the reader of the title of this PR to guess?

[Curts0]

Updated title. I enjoy making people guess. Or was maybe hoping for some clickbait to push the viewer to click on it.