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/Systems/437XR1138R2/LogServices/Log1/index.json

@@ -0,0 +1,24 @@
+{
+    "@odata.type": "#LogService.v1_9_0.LogService",
+    "Id": "Log1",
+    "Name": "System Log Service",
+    "MaxNumberOfRecords": 1000,
+    "OverWritePolicy": "WrapsWhenFull",
+    "DateTime": "2015-03-13T04:14:33+06:00",
+    "DateTimeLocalOffset": "+06:00",
+    "ServiceEnabled": true,
+    "Status": {
+        "State": "Enabled",
+        "Health": "OK"
+    },
+    "Actions": {
+        "#LogService.ClearLog": {
+            "target": "/redfish/v1/Systems/437XR1138R2/LogServices/Log1/Actions/LogService.ClearLog"
+        }
+    },
+    "Entries": {
+        "@odata.id": "/redfish/v1/Systems/437XR1138R2/LogServices/Log1/Entries"
+    },
+    "@odata.id": "/redfish/v1/Systems/437XR1138R2/LogServices/Log1",
+    "@Redfish.Copyright": "Copyright 2014-2026 DMTF. For the full DMTF copyright policy, see http://www.dmtf.org/about/policies/copyright."
+}