fix: submodule packaging for bazel (#4643)

src/phoenix/__init__.py

@@ -31,6 +31,11 @@
   - Explore model performance, drift, and data quality metrics
 """
 
+# The following line is needed to ensure that other modules using the
+# `phoenix.*` path can be discovered by Bazel. For details,
+# see: https://github.com/Arize-ai/openinference/issues/398
+__path__ = __import__("pkgutil").extend_path(__path__, __name__)
+
 __all__ = [
     "__version__",
     "active_session",