feat: Allow ResourceContents objects to be returned directly from read_resource handlers

Updated the low-level server's read_resource decorator to accept TextResourceContents
and BlobResourceContents objects directly, in addition to the existing ReadResourceContents.
This provides more flexibility for resource handlers to construct and return properly
typed ResourceContents objects with full control over all properties.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: alexanderreiff

src/mcp/server/lowlevel/server.py

@@ -311,7 +311,14 @@ async def handler(_: Any):
 
     def read_resource(self):
         def decorator(
-            func: Callable[[AnyUrl], Awaitable[str | bytes | Iterable[ReadResourceContents]]],
+            func: Callable[
+                [AnyUrl],
+                Awaitable[
+                    str
+                    | bytes
+                    | Iterable[ReadResourceContents | types.TextResourceContents | types.BlobResourceContents]
+                ],
+            ],
         ):
             logger.debug("Registering handler for ReadResourceRequest")
 
@@ -346,7 +353,10 @@ def create_content(data: str | bytes, mime_type: str | None):
                         content = create_content(data, None)
                     case Iterable() as contents:
                         contents_list = [
-                            create_content(content_item.content, content_item.mime_type) for content_item in contents
+                            content_item
+                            if isinstance(content_item, types.ResourceContents)
+                            else create_content(content_item.content, content_item.mime_type)
+                            for content_item in contents
                         ]
                         return types.ServerResult(
                             types.ReadResourceResult(