Add Promptkit definition conformance coverage

testdata/promptkit-v0.9/profiles/custom-base.yaml

@@ -0,0 +1,16 @@
+id: custom-base
+backend: fixture-custom
+model: fixture-base-model
+temperature: 0.25
+max_tokens: 640
+top_p: 0.9
+timeout_seconds: 45
+service_tier: flex
+reasoning_effort: medium
+api_key_env: FIXTURE_PROFILE_API_KEY
+extra_params:
+  routing:
+    order:
+      - primary
+      - fallback
+    allow_fallback: true

testdata/promptkit-v0.9/profiles/custom-derived.yml

@@ -0,0 +1,4 @@
+id: custom-derived
+base_profile: custom-base
+model: fixture-derived-model
+reasoning_effort: high

testdata/promptkit-v0.9/profiles/endpoint-only.yaml

@@ -0,0 +1,10 @@
+id: endpoint-only
+endpoint: http://127.0.0.1:8000/v1
+model: fixture-endpoint-model
+temperature: 0.1
+max_tokens: 128
+top_p: 0.75
+timeout_seconds: 30
+extra_params:
+  endpoint_option:
+    nested: true