refactor: res.download with lower complexity

[criszst]

Description

This PR refactors the res.download function to reduce complexity and improve readability while maintaining existing functionality.

Changes

• Simplified argument extraction logic using modern JavaScript methods
• Replaced multiple if-else statements with more concise alternatives
• Utilized ES6+ features like arrow functions and Object.assign
• Improved code organization for better maintainability
• Add examples and params types on DOCS

Motivation and Context

The existing implementation of res.download was functional but complex (with multiple nested conditions). This refactor aims to make the code more straightforward and easier to understand, which should aid in future maintenance and reduce the likelihood of bugs.

How Has This Been Tested?

• Ran existing test suite to ensure no regression

Additional Notes

This refactor doesn't change the function's API or behavior, so it should be a low-risk change. However, thorough review and testing are appreciated to ensure no edge cases have been overlooked ☺️
By the way, I believe it is possible to refactor further, but I don't want to risk it before this pull-request