Optimize the site, the animation and the gradients.

[teo-tsirpanis]

This PR:

• Replaces setInterval with requestAnimationFrame, which is more efficient and handles displays of various refresh rates.
• Uses HTML 5 linear gradients, which look much better than the previous manual logic.
• Optimizes the code a bit, including adding a type annotation for the variable holding the canvas, which enables auto-completion in editors.
• Adds some extra tags that improve SEO (the site now has a perfect Lighthouse score), and specifies the year the site won the prize.

You can preview the new site in https://teo-tsirpanis.github.io/Dual-Axis-Illusion/