Add DMTF mockup fixtures and test helpers

Unmodified files from DMTF Redfish-Publications (public-rackmount1, public-localstorage, public-telemetry), only those the tests use, each set with DMTF's BSD-3-Clause license and a COMMANDS.txt naming the source commit and request paths.

conftest.py loads them by request path and serves a mockup over mocked HTTP, with a SessionService that hands out a token, for the transport tests.

tests/fixtures/dmtf-public-localstorage/Systems/437XR1138R2/Storage/index.json

@@ -0,0 +1,12 @@
+{
+    "@odata.type": "#StorageCollection.StorageCollection",
+    "Name": "Storage Collection",
+    "Members@odata.count": 1,
+    "Members": [
+        {
+            "@odata.id": "/redfish/v1/Systems/437XR1138R2/Storage/1"
+        }
+    ],
+    "@odata.id": "/redfish/v1/Systems/437XR1138R2/Storage",
+    "@Redfish.Copyright": "Copyright 2014-2026 DMTF. For the full DMTF copyright policy, see http://www.dmtf.org/about/policies/copyright."
+}