WIP: Add Uri extension documentation

[jordikroon]

Add comprehensive documentation for the new Uri extension, which implements RFC 3986 and WHATWG URL Standard specifications.

Includes:

• Uri\Rfc3986\Uri class with RFC 3986 compliant URI parsing and manipulation
• Uri\UriComparisonMode enum for flexible URI comparison options
• Complete method reference for all Uri\Rfc3986\Uri getters, setters, and utility methods
• Version information indicating availability in PHP 8.5.0+

This is a Work In Progress.