[mojo][io] Magic to Pixi + replaced IO backend with numpy

[shivasankarka]

This PR brings new minor changes.

• Switch from magic to pixi. Any command that involved the word 'magic' should be replaced with 'pixi'.
• Replaced io backend ('load', 'save' etc) with numpy since it's a dependancy already. More functions will be added in later updates. Added basic test files for load and save.

[forfudan]

I ignored the pixi.lock in the .gitignore.