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/Chassis/1U/Sensors/CPUFan1/index.json

@@ -0,0 +1,36 @@
+{
+    "@odata.type": "#Sensor.v1_14_0.Sensor",
+    "Id": "CPUFan1",
+    "Name": "CPU #1 Fan Speed",
+    "PhysicalContext": "CPU",
+    "Reading": 45,
+    "SpeedRPM": 1490,
+    "ReadingRangeMax": 100,
+    "ReadingRangeMin": 0,
+    "ReadingType": "Percent",
+    "ReadingUnits": "%",
+    "Status": {
+        "Health": "OK",
+        "State": "Enabled"
+    },
+    "Thresholds": {
+        "LowerCaution": {
+            "Reading": 5,
+            "DwellTime": "PT30S",
+            "Activation": "Decreasing",
+            "HysteresisReading": 2,
+            "HysteresisDuration": "PT1M",
+            "@Redfish.WriteableProperties": []
+        },
+        "LowerCritical": {
+            "Reading": 0,
+            "DwellTime": "PT10S",
+            "Activation": "Decreasing",
+            "HysteresisReading": 2,
+            "HysteresisDuration": "PT1M",
+            "@Redfish.WriteableProperties": []
+        }
+    },
+    "@odata.id": "/redfish/v1/Chassis/1U/Sensors/CPUFan1",
+    "@Redfish.Copyright": "Copyright 2014-2026 DMTF. For the full DMTF copyright policy, see http://www.dmtf.org/about/policies/copyright."
+}