feat: introduce API leveling, post_training to v1alpha

Rather than have a single `LLAMA_STACK_VERSION`, we need to have a `_V1`, `_V1ALPHA`, and `_V1BETA` constant.

This also necessitated addition of `level` to the `WebMethod` so that routing can be handeled properly.

For backwards compat, the `v1` routes are being kept around and marked as `deprecated`. When used, the server will log a deprecation warning.

move:

post_training to v1alpha as it is under heavy development and not near its final state
eval: job scheduling is not implemented. Relies heavily on the datasetio API which is under development missing implementations of specific routes indicating the structure of those routes might change. Additionally eval depends on the inference API which is going to be deprecated, eval will likely need a major API surface change to conform to using completions properly

Signed-off-by: Charlie Doern <cdoern@redhat.com>

llama_stack/core/server/tracing.py

@@ -45,6 +45,14 @@ class TracingMiddleware:
             logger.debug(f"No matching route found for path: {path}, falling back to FastAPI")
             return await self.app(scope, receive, send)
 
+        # Log deprecation warning if route is deprecated
+        if getattr(webmethod, "deprecated", False):
+            logger.warning(
+                f"DEPRECATED ROUTE USED: {scope.get('method', 'GET')} {path} - "
+                f"This route is deprecated and may be removed in a future version. "
+                f"Please check the docs for the supported version."
+            )
+
         trace_attributes = {"__location__": "server", "raw_path": path}
 
         # Extract W3C trace context headers and store as trace attributes