Fix dependency configuration and Python compatibility for helloworld_with_ratelimiter

- Updated pyproject.toml to use uv.sources for local ratelimiter-ext dependency
- Added tool.hatch.metadata.allow-direct-references configuration
- Added .python-version file (gitignored) to ensure Python 3.12 compatibility
- Resolved build issues with pydantic-core and ormsgpack on Python 3.14

Author: madankumarpichamuthu

samples/python/agents/helloworld_with_ratelimiter/pyproject.toml

@@ -16,13 +16,19 @@ dependencies = [
     "sse-starlette>=2.3.5",
     "starlette>=0.46.2",
     "uvicorn>=0.34.2",
-    "ratelimiter-ext @ file://../../extensions/ratelimiter",
+    "ratelimiter-ext",
 ]
 
+[tool.uv.sources]
+ratelimiter-ext = { path = "../../extensions/ratelimiter", editable = true }
+
 [project.optional-dependencies]
 ratelimiter = [
 ]
 
+[tool.hatch.metadata]
+allow-direct-references = true
+
 [tool.hatch.build.targets.wheel]
 packages = ["."]