Added Count Inversions algorithm (Merge Sort based)

[usman-7455]

Describe your change:

• Add an algorithm

This pull request adds a Python implementation of the Count Inversions algorithm using a modified Merge Sort approach.

Count Inversions is used to determine how far an array is from being sorted by counting the number of out-of-order pairs (i, j) such that i < j and arr[i] > arr[j]. This has applications in ranking systems, bioinformatics, and measuring list similarity.

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, I am not combining unrelated changes.
• All new Python files are placed inside an existing directory.
• All filenames are in all lowercase characters with no spaces or dashes. (Note: The filename is Count_Inversion.py; I can rename it to count_inversion.py if needed.)
• 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.

Wikipedia link: https://en.wikipedia.org/wiki/Inversion_(discrete_mathematics)

[mindaugl]

Would be appropriate to change interface and return both sorted array and number of inversions (currently 'count_inverstions()' returns only number of inversions). For counting inversions, there is no need to construct new sorted array, and the algorithm is simpler. Also, would be appropriate to change the name of file to, e.g., merge_count_inversions_sort.py.