Overhaul of Resources (#125)

* Supporting resource templates with read resource callback

Fixes #123

* Aligning the resource data structures with the 2024-11-05 schema

- Introducing separate classes for Text and Blob ResourceContents
- Custom JSON converter to allow those types to be returned, making it easier to follow the type system against the spec
- Updated tests

* Apply suggestions from code review

Co-authored-by: Stephen Toub <stoub@microsoft.com>
Co-authored-by: Peder Holdgaard Pedersen <127606677+PederHP@users.noreply.github.com>

* Putting files back where they belong

* Adding an internal constructor to prevent overloads

* Addressing feedback

* Apply suggestions from code review

Co-authored-by: Stephen Toub <stoub@microsoft.com>

* Update src/ModelContextProtocol/Protocol/Types/ResourceContents.cs

* Addressing feedback

---------

Co-authored-by: Stephen Toub <stoub@microsoft.com>
Co-authored-by: Peder Holdgaard Pedersen <127606677+PederHP@users.noreply.github.com>

tests/ModelContextProtocol.TestSseServer/Program.cs

@@ -81,7 +81,7 @@ public class Program
                     Name = $"Resource {i + 1}",
                     MimeType = "text/plain"
                 });
-                resourceContents.Add(new ResourceContents()
+                resourceContents.Add(new TextResourceContents()
                 {
                     Uri = uri,
                     MimeType = "text/plain",
@@ -97,7 +97,7 @@ public class Program
                     Name = $"Resource {i + 1}",
                     MimeType = "application/octet-stream"
                 });
-                resourceContents.Add(new ResourceContents()
+                resourceContents.Add(new BlobResourceContents()
                 {
                     Uri = uri,
                     MimeType = "application/octet-stream",
@@ -262,7 +262,7 @@ public class Program
                         return Task.FromResult(new ReadResourceResult()
                         {
                             Contents = [
-                                new ResourceContents()
+                                new TextResourceContents()
                                 {
                                     Uri = request.Params.Uri,
                                     MimeType = "text/plain",