Migrate to manifest V3 for Chrome, update tech stack, major refactoring

[alvkn]

As I've noted here, Firefox barely supports manifest v3 (there are some issues with service workers), and there are many ways to handle the separation of manifests for different browsers - and this is one of them.

What was done:
I did a major refactoring, removed obsolete (in my opinion) libs like browserify and others.

Vite is chosen as the bundler to provide an easy and robust way to build the extension without having to manually copy files (except the license file).

Mocha is replaced by Vitest to eliminate the need to compile TypeScript-based tests before running - API is almost the same

vite-plugin-web-extension plugin is used to handle different manifest versions in the most optimal way (in my opinion).

Also, updated the code to use modern JS approaches (const and let instead of var), applied code formatting, unified indent size across the codebase.

Fixes #34