test: add sample fixtures for testing

- _demo.log: sample log file for log_analyzer.py
- _demo_openapi.json: sample OpenAPI spec for api_test_generator.py

Author: Michspirit99

samples/_demo.log

@@ -0,0 +1,10 @@
+2026-02-07 12:00:00 INFO Service starting
+2026-02-07 12:00:01 INFO Listening on port=8080
+2026-02-07 12:01:00 WARN Cache miss key=user:123
+2026-02-07 12:01:05 ERROR Failed to connect to db host=db1 timeout=5s
+2026-02-07 12:01:06 INFO Retrying db connection
+2026-02-07 12:01:12 INFO Connected to db
+2026-02-07 12:02:00 WARN Slow query duration_ms=1200 query="SELECT * FROM orders"
+2026-02-07 12:03:00 INFO Request id=abc123 status=200 latency_ms=34
+2026-02-07 12:03:05 INFO Request id=abc124 status=500 latency_ms=20
+2026-02-07 12:03:05 ERROR Unhandled exception trace_id=zzz999

samples/_demo_openapi.json

@@ -0,0 +1,25 @@
+{
+  "openapi": "3.0.0",
+  "info": {"title": "Demo API", "version": "1.0.0"},
+  "paths": {
+    "/health": {
+      "get": {
+        "responses": {
+          "200": {"description": "OK"}
+        }
+      }
+    },
+    "/users": {
+      "post": {
+        "requestBody": {
+          "content": {
+            "application/json": {
+              "schema": {"type": "object", "properties": {"name": {"type": "string"}}}
+            }
+          }
+        },
+        "responses": {"201": {"description": "Created"}}
+      }
+    }
+  }
+}