[router] add py binding unit tests to coverage 80% (#10043)

sgl-router/py_test/unit/__init__.py

@@ -0,0 +1,7 @@
+"""
+Unit tests for sglang_router.
+
+This package contains fast, isolated unit tests for Python components
+of the SGLang router. These tests focus on testing individual functions
+and classes in isolation without starting actual router instances.
+"""