Significantly simpler and malleable test setup (#360)

* Significantly simpler and malleable test setup

* convert memory tests

* refactor fixtures and add support for composable fixtures

* Fix memory to use the newer fixture organization

* Get agents tests working

* Safety tests work

* yet another refactor to make this more general

now it accepts --inference-model, --safety-model options also

* get multiple providers working for meta-reference (for inference + safety)

* Add README.md

---------

Co-authored-by: Ashwin Bharambe <ashwin@meta.com>

llama_stack/providers/tests/env.py

@@ -0,0 +1,24 @@
+# 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.
+
+import os
+
+
+class MissingCredentialError(Exception):
+    pass
+
+
+def get_env_or_fail(key: str) -> str:
+    """Get environment variable or raise helpful error"""
+    value = os.getenv(key)
+    if not value:
+        raise MissingCredentialError(
+            f"\nMissing {key} in environment. Please set it using one of these methods:"
+            f"\n1. Export in shell: export {key}=your-key"
+            f"\n2. Create .env file in project root with: {key}=your-key"
+            f"\n3. Pass directly to pytest: pytest --env {key}=your-key"
+        )
+    return value