K nearest neighbors Algorithm

[haswanth10]

This commit adds K-nearest neighbors Algorithm.

Important points regarding Commit:

1. Euclidean distance is used to compute the distance between 2 points.
2. Only classification has been implemented by using majority vote amongst k nearest neighbors for an input point
3. An Enum has been created for distance computation so that it can be extended to other distance computation techniques/formulae like Manhattan Distance, etc.
4. Classification Label is of type 'String'.

Pull Request Template

Description

Please include a summary of the change and which issue (if any) is fixed. A brief description of the algorithm and your implementation method can be helpful too. If the implemented method/algorithm is not so well-known, it would be helpful to add a link to an article explaining it with more details.

Type of change

Please delete options that are not relevant.

• [ Y] New feature (non-breaking change which adds functionality)

Checklist:

• [ Y] I ran bellow commands using the latest version of rust nightly.
• [ Y] I ran cargo clippy --all -- -D warnings just before my last commit and fixed any issue that was found.
• [ Y] I ran cargo fmt just before my last commit.
• [Y ] I ran cargo test just before my last commit and all tests passed.
• [ Y] I added my algorithm to the corresponding mod.rs file within its own folder, and in any parent folder(s).
• [ Y] I added my algorithm to DIRECTORY.md with the correct link.
• [ Y] I checked COUNTRIBUTING.md and my code follows its guidelines.

Please make sure that if there is a test that takes too long to run ( > 300ms), you #[ignore] that or try to optimize your code or make the test easier to run. We have this rule because we have hundreds of tests to run; If each one of them took 300ms, we would have to wait for a long time.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 99.56897% with 1 line in your changes missing coverage. Please review.

Project coverage is 95.07%. Comparing base (0b8ba06) to head (56bd101).

Files	Patch %	Lines
...chine_learning/optimization/k_nearest_neighbors.rs	99.56%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #723 +/- ## ========================================== + Coverage 95.02% 95.07% +0.04% ========================================== Files 303 304 +1 Lines 22577 22809 +232 ========================================== + Hits 21454 21685 +231 - Misses 1123 1124 +1 ```

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[haswanth10]

Hi , i made the changes suggested. Let me know if there is anything else that's needed :)