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-rackmount1/SessionService/Sessions/index.json

@@ -0,0 +1,15 @@
+{
+    "@odata.type": "#SessionCollection.SessionCollection",
+    "Name": "Session Collection",
+    "Members@odata.count": 2,
+    "Members": [
+        {
+            "@odata.id": "/redfish/v1/SessionService/Sessions/1234567890ABCDEF"
+        },
+        {
+            "@odata.id": "/redfish/v1/SessionService/Sessions/1234567890ABCDEG"
+        }
+    ],
+    "@odata.id": "/redfish/v1/SessionService/Sessions",
+    "@Redfish.Copyright": "Copyright 2014-2026 DMTF. For the full DMTF copyright policy, see http://www.dmtf.org/about/policies/copyright."
+}

tests/fixtures/dmtf-public-rackmount1/SessionService/index.json

@@ -0,0 +1,19 @@
+{
+    "@odata.type": "#SessionService.v1_2_0.SessionService",
+    "Id": "SessionService",
+    "Name": "Session Service",
+    "Description": "Session Service",
+    "Status": {
+        "State": "Enabled",
+        "Health": "OK"
+    },
+    "ServiceEnabled": true,
+    "SessionTimeout": 30,
+    "AbsoluteSessionTimeout": 3600,
+    "AbsoluteSessionTimeoutEnabled": true,
+    "Sessions": {
+        "@odata.id": "/redfish/v1/SessionService/Sessions"
+    },
+    "@odata.id": "/redfish/v1/SessionService",
+    "@Redfish.Copyright": "Copyright 2014-2026 DMTF. For the full DMTF copyright policy, see http://www.dmtf.org/about/policies/copyright."
+}