Changes Made

• Added the implementation of E91 QKD Protocol using the 'qiskit' library.
• Returned the values given a predefined value for the number of bits used for the simulation.
• Generated entangled Bell pairs for Alice and Bob, followed by random selection of measurement bases by both parties.
• Measurement of quantum states was performed using the 'qiskit-aer' library. This was followed by Basis Sifting.
• Performed a CHSH inequality test to detect the presence of an eavesdropper (Eve).
• Provided a clear demonstration of the protocol's outcome, returning Alice's key, Bob's key, the CHSH value, and a final check to verify if the keys match and are secure.
• Ensured the code follows the mentioned contribution guidelines, along with doctests.

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• 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.
• I know that pull requests will not be merged if they fail the automated tests.
• 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".