Fix URI template derivation and lookup (#530)

* Use lowercase host in resource URI template derivation.

* Address feedback

* Add casing testing for non-templated resource lookups.

* Fix uri primitive lookup

* Use a hardcoded mcp hostname in derived resource template URIs and ensure built-in resources work with the VS Code client.

* Address feedback

* Fix equality comparison

* Use dedicated type for resource collections.

src/ModelContextProtocol.Core/Server/McpServerResourceCollection.cs

@@ -0,0 +1,5 @@
+namespace ModelContextProtocol.Server;
+
+/// <summary>Provides a thread-safe collection of <see cref="McpServerResource"/> instances, indexed by their URI templates.</summary>
+public sealed class McpServerResourceCollection()
+    : McpServerPrimitiveCollection<McpServerResource>(UriTemplate.UriTemplateComparer.Instance);