[refactor]: optimize matrix operations in MLP

[docs]: update README.md to reflect library name change to 'dixon' and enhance usage instructions; add notes on best practices for MNIST results

[refactor]: rename package from primitive_ml to dixon; update dependencies and enhance main.rs with error handling for model loading

[refactor]: remove iris.csv and update main.rs to use new data path; enhance MLP with gradient computation and backpropagation methods

[feat]: inital commit and project setup