fix(samples): merge testcase.yaml into sample.yaml for Zephyr v4 Twister

Zephyr v4.4.0 Twister requires sample.yaml to contain a 'tests' section.
Having a separate testcase.yaml alongside sample.yaml causes Twister to
validate sample.yaml alone (which lacks 'tests:'), resulting in
ValidationError and the entire sample directory being skipped.

Merged the tests: block from each testcase.yaml into the corresponding
sample.yaml, and removed the now-redundant testcase.yaml files.
All 17 samples updated.

Co-Authored-By: Oz <oz-agent@warp.dev>

Author: tbitcs

samples/access_control/sample.yaml

@@ -8,3 +8,10 @@ common:
   tags: arbiter reasoning cors auth security api iot
   harness: console
   platform_allow: native_sim
+tests:
+  sample.arbiter.access-control:
+    tags: arbiter sample
+    platform_allow: native_sim
+    harness: console
+    build_only: true
+

samples/access_control/testcase.yaml

@@ -5,3 +5,10 @@ common:
   tags: arbiter reasoning safety
   harness: console
   platform_allow: native_sim
+tests:
+  sample.arbiter.battery-policy:
+    tags: arbiter sample
+    platform_allow: native_sim
+    harness: console
+    build_only: true
+

samples/battery_policy/sample.yaml

@@ -9,3 +9,10 @@ common:
   tags: arbiter reasoning safety cobot robotics iso-10218
   harness: console
   platform_allow: native_sim
+tests:
+  sample.arbiter.cobot-safety:
+    tags: arbiter sample
+    platform_allow: native_sim
+    harness: console
+    build_only: true
+

samples/battery_policy/testcase.yaml

@@ -9,3 +9,10 @@ common:
   tags: arbiter solver diagnostics fault-tree motor-drive
   harness: console
   platform_allow: native_sim
+tests:
+  sample.arbiter.fault-diagnosis:
+    tags: arbiter sample solver
+    platform_allow: native_sim
+    harness: console
+    build_only: true
+

samples/cobot_safety/sample.yaml

@@ -9,3 +9,10 @@ common:
   tags: arbiter reasoning firewall security network iot
   harness: console
   platform_allow: native_sim
+tests:
+  sample.arbiter.firewall-policy:
+    tags: arbiter sample
+    platform_allow: native_sim
+    harness: console
+    build_only: true
+