refactor: Enhance code quality and cli module

[MrFixThis]

Improved screenshot capturing logic, enhanced helper functions and improved CLI argument parsing specification

[MrFixThis]

Days ago I came across this project and I really like its concept, so here are some general improvements I made to the application.

Some of them are:

• Improved cli argument parsing specification.
• Some unit tests added to the args submodule.
• Improved code readability and quality of the screenshot module.
• Removed unnecessary heap alloctions for errors using anyhow crate.

All these details translate into better quality and speed.

[MrFixThis]

I almost forgot. I've updated the README.md to add the new --file-path | -f positional argument in the section where the functionality to read the contents of a file is shown.

Please update the example screenshot.

[pwnwriter]

Hey @MrFixThis,

Thanks a ton for your help! You've really stepped up the game of HXN. awesome! Let's get that pr merged 😻

Cheers!