fix(client/python): reachable cert-validation flag; bounded off-loop TOFU probe; license/marker fixes (Client.Python-027..031)

clients/python/pyproject.toml

@@ -16,11 +16,10 @@ dependencies = [
 authors = [
   { name = "Joseph Doherty" },
 ]
-license = { text = "Proprietary" }
+license = "LicenseRef-Proprietary"
 keywords = ["mxaccess", "mxgateway", "grpc", "client", "archestra"]
 classifiers = [
   "Development Status :: 3 - Alpha",
-  "License :: Other/Proprietary License",
   "Programming Language :: Python :: 3",
   "Programming Language :: Python :: 3.12",
   "Programming Language :: Python :: 3.13",
@@ -54,3 +53,6 @@ where = ["src"]
 addopts = "-ra"
 pythonpath = ["src"]
 testpaths = ["tests"]
+markers = [
+  "tls: loopback TLS tests, opt-in via MXGATEWAY_RUN_TLS_TESTS=1",
+]