Contributes to #9943 with monotonic_array.py

[MelihMSahin]

Contributes to #9943 by adding doctests, including negative numbers and an array of same integers.

Describe your change:

• Add an algorithm? No
• Fix a bug or typo in an existing algorithm? No
• Add or change doctests? I have added doctests, imported doctest and called the doctest function in if name ==...
• Documentation change? No

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new Python files are placed inside an existing directory.
• All filenames are in all lowercase characters with no spaces or dashes.
• All functions and variable names follow Python naming conventions.
• All function parameters and return values are annotated with Python type hints.
• All functions have doctests that pass the automated testing.
• All new algorithms include at least one URL that points to Wikipedia or another similar explanation.
• If this pull request resolves one or more open issues then the description above includes the issue number(s) with a closing keyword: "Fixes #ISSUE-NUMBER".