feat(isolated): add factory module for isolated API instances

Signed-off-by: marcozabel <marco.zabel@dynatrace.com>

Author: marcozabel

openfeature/isolated.py

@@ -0,0 +1,37 @@
+"""Factory for creating isolated OpenFeature API instances.
+
+Per specification requirement 1.8.3, this module is intentionally separate
+from the global singleton ``openfeature.api`` to reduce the risk of
+accidentally creating isolated instances when the singleton is appropriate.
+
+Usage::
+
+    from openfeature.isolated import create_api
+
+    api = create_api()
+    api.set_provider(MyProvider())
+    client = api.get_client()
+
+Each instance returned by :func:`create_api` maintains its own providers,
+evaluation context, hooks, event handlers, and transaction context propagator
+— fully independent from the global singleton and from other instances.
+
+A single provider instance should not be registered with more than one API
+instance simultaneously (spec requirement 1.8.4).
+"""
+
+from openfeature._api import OpenFeatureAPI
+
+__all__ = ["OpenFeatureAPI", "create_api"]
+
+
+def create_api() -> OpenFeatureAPI:
+    """Create a new, independent OpenFeature API instance.
+
+    The returned instance is functionally equivalent to the global singleton
+    (``openfeature.api``), but with completely isolated state.
+
+    Returns:
+        A new :class:`OpenFeatureAPI` instance.
+    """
+    return OpenFeatureAPI()