PDSls Redirector per DrearyWillow

Previous versions of PDSls Redirector (v1.0.0 - v1.0.8) relied on looping over a list of regular expressions to match URL patterns, using capture groups to extract variables. This approach was inefficient, difficult to maintain, and prone to errors. Additionally, all extension logic was contained within a single, unwieldy background.js file.

This PR introduces a modular architecture leveraging built-in JavaScript URL parsing instead of regex-based pattern matching.

• Modular Design: Each Handler and Resolver now has its own file, improving code readability and scalability.
• Handlers/Resolvers are now indexed by hostname, reducing lookup time.
• Added Handler/Resolver unit testing, enabling bulk validation and reducing unintended breakages.
• Better Documentation: Includes contribution guidelines, testing procedures, and a list of supported sites.

This refactor should simplify site additions, improve maintainability, and just generally be nicer to work with.