Update simple-resource example to use non-deprecated read_resource return type

Changed the read_resource handler to return Iterable[ReadResourceContents]
instead of a plain string, following the recommended pattern and avoiding
deprecation warnings.

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

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

Author: pja-ant

examples/servers/simple-resource/mcp_simple_resource/server.py

@@ -2,6 +2,7 @@
 import click
 import mcp.types as types
 from mcp.server.lowlevel import Server
+from mcp.server.lowlevel.helper_types import ReadResourceContents
 from pydantic import AnyUrl, FileUrl
 from starlette.requests import Request
 
@@ -46,15 +47,15 @@ async def list_resources() -> list[types.Resource]:
         ]
 
     @app.read_resource()
-    async def read_resource(uri: AnyUrl) -> str | bytes:
+    async def read_resource(uri: AnyUrl):
         if uri.path is None:
             raise ValueError(f"Invalid resource path: {uri}")
         name = uri.path.replace(".txt", "").lstrip("/")
 
         if name not in SAMPLE_RESOURCES:
             raise ValueError(f"Unknown resource: {uri}")
 
-        return SAMPLE_RESOURCES[name]["content"]
+        return [ReadResourceContents(content=SAMPLE_RESOURCES[name]["content"], mime_type="text/plain")]
 
     if transport == "sse":
         from mcp.server.sse import SseServerTransport