fix: allow URIs without double slash in Resource and ResourceTemplate (RFC 3986)

[blackwell-systems]

Summary

The URI regex in Resource and ResourceTemplate requires :// after the scheme, rejecting valid URIs where the hier-part does not start with //. Per RFC 3986, the authority component (and its // prefix) is optional.

What breaks

// All of these throw InvalidArgumentException:
new Resource(uri: 'urn:isbn:0451450523', name: 'book');
new Resource(uri: 'mailto:user@example.com', name: 'contact');
new Resource(uri: 'data:text/plain;base64,SGVsbG8=', name: 'data');
new Resource(uri: 'config:myapp/settings', name: 'settings');

new ResourceTemplate(uriTemplate: 'config:{key}', name: 'config');

The MCP spec allows custom URI schemes following RFC 3986.

Fix

Changed :// to : in both regex patterns:

- '/^[a-zA-Z][a-zA-Z0-9+.-]*:\/\/[^\s]*$/'
+ '/^[a-zA-Z][a-zA-Z0-9+.-]*:[^\s]*$/'

- '/^[a-zA-Z][a-zA-Z0-9+.-]*:\/\/.*{[^{}]+}.*/'
+ '/^[a-zA-Z][a-zA-Z0-9+.-]*:.*{[^{}]+}.*/'

URIs with :// (like file://path) continue to match.

Test plan

• Added data-provider tests for urn:, mailto:, data:, and custom schemes without //
• Added data-provider tests for resource templates without //
• All 20 tests pass (phpunit tests/Unit/Schema/)
• Existing tests unchanged

Fixes #293