chore: move all Llama Stack types from llama-models to llama-stack (#1098)

llama-models should have extremely minimal cruft. Its sole purpose
should be didactic -- show the simplest implementation of the llama
models and document the prompt formats, etc.

This PR is the complement to
https://github.com/meta-llama/llama-models/pull/279

## Test Plan

Ensure all `llama` CLI `model` sub-commands work:

```bash
llama model list
llama model download --model-id ...
llama model prompt-format -m ...
```

Ran tests:
```bash
cd tests/client-sdk
LLAMA_STACK_CONFIG=fireworks pytest -s -v inference/
LLAMA_STACK_CONFIG=fireworks pytest -s -v vector_io/
LLAMA_STACK_CONFIG=fireworks pytest -s -v agents/
```

Create a fresh venv `uv venv && source .venv/bin/activate` and run
`llama stack build --template fireworks --image-type venv` followed by
`llama stack run together --image-type venv` <-- the server runs

Also checked that the OpenAPI generator can run and there is no change
in the generated files as a result.

```bash
cd docs/openapi_generator
sh run_openapi_generator.sh
```

llama_stack/strong_typing/slots.py

@@ -0,0 +1,27 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+from typing import Any, Dict, Tuple, Type, TypeVar
+
+T = TypeVar("T")
+
+
+class SlotsMeta(type):
+    def __new__(cls: Type[T], name: str, bases: Tuple[type, ...], ns: Dict[str, Any]) -> T:
+        # caller may have already provided slots, in which case just retain them and keep going
+        slots: Tuple[str, ...] = ns.get("__slots__", ())
+
+        # add fields with type annotations to slots
+        annotations: Dict[str, Any] = ns.get("__annotations__", {})
+        members = tuple(member for member in annotations.keys() if member not in slots)
+
+        # assign slots
+        ns["__slots__"] = slots + tuple(members)
+        return super().__new__(cls, name, bases, ns)  # type: ignore
+
+
+class Slots(metaclass=SlotsMeta):
+    pass