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/Chassis/1U/index.json

@@ -0,0 +1,46 @@
+{
+    "@odata.type": "#Chassis.v1_29_0.Chassis",
+    "Id": "1U",
+    "Name": "Computer System Chassis",
+    "ChassisType": "RackMount",
+    "AssetTag": "Chicago-45Z-2381",
+    "Manufacturer": "Contoso",
+    "Model": "3500RX",
+    "SKU": "8675309",
+    "SerialNumber": "437XR1138R2",
+    "PartNumber": "224071-J23",
+    "PowerState": "On",
+    "IndicatorLED": "Lit",
+    "Status": {
+        "State": "Enabled",
+        "Health": "OK"
+    },
+    "Thermal": {
+        "@odata.id": "/redfish/v1/Chassis/1U/Thermal"
+    },
+    "Power": {
+        "@odata.id": "/redfish/v1/Chassis/1U/Power"
+    },
+    "Drives": {
+        "@odata.id": "/redfish/v1/Chassis/1U/Drives"
+    },
+    "Links": {
+        "ComputerSystems": [
+            {
+                "@odata.id": "/redfish/v1/Systems/437XR1138R2"
+            }
+        ],
+        "ManagedBy": [
+            {
+                "@odata.id": "/redfish/v1/Managers/BMC"
+            }
+        ],
+        "ManagersInChassis": [
+            {
+                "@odata.id": "/redfish/v1/Managers/BMC"
+            }
+        ]
+    },
+    "@odata.id": "/redfish/v1/Chassis/1U",
+    "@Redfish.Copyright": "Copyright 2014-2026 DMTF. For the full DMTF copyright policy, see http://www.dmtf.org/about/policies/copyright."
+}