Added Momentum Optimizer to 'optimization' in machine-learning

[showmyth]

Pull Request Template

Description

This PR adds the Momentum optimizater to the optimization module.

Momentum accelerates gradient descent by accumulating past gradients into a velocity vector, leading to faster and more stable convergence.

Update equations:

• velocity_{k+1} = beta * velocity_k + gradient(x_k)
• x_{k+1} = x_k - learning_rate * velocity_{k+1}

For more information, checkout Momentum Optimization by CS231

Type of change

Please delete options that are not relevant.

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

Checklist:

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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.34%. Comparing base (a8491ae) to head (1933f5e).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #933      +/-   ##
==========================================
+ Coverage   95.32%   95.34%   +0.01%     
==========================================
  Files         319      320       +1     
  Lines       20895    20970      +75     
==========================================
+ Hits        19919    19994      +75     
  Misses        976      976              

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[showmyth]

Hey @siriak, would be grateful if you could review this as per your convinience.

[siriak]

Looks good, thanks!