switch to cargo-insta for snapshot testing

tests/snapshots/tests__small.dem.snap

@@ -0,0 +1,49 @@
+---
+source: tests/tests.rs
+expression: state
+---
+{
+  "players": [
+    {
+      "entity": 1,
+      "position": {
+        "x": -3599.1775,
+        "y": 421.331,
+        "z": 298.0
+      },
+      "health": 125,
+      "max_health": 125,
+      "class": "scout",
+      "team": "red",
+      "view_angle": 0.0,
+      "pitch_angle": 0.35294342,
+      "state": "Alive",
+      "info": {
+        "classes": {},
+        "name": "Icewind | demos.tf",
+        "userId": 2,
+        "steamId": "[U:1:64229260]",
+        "team": "other"
+      },
+      "charge": 0,
+      "simtime": 78,
+      "ping": 5,
+      "in_pvs": true
+    }
+  ],
+  "buildings": {},
+  "world": {
+    "boundary_min": {
+      "x": -3882.0,
+      "y": -4570.0,
+      "z": -560.0
+    },
+    "boundary_max": {
+      "x": 5240.0,
+      "y": 3936.0,
+      "z": 1641.0
+    }
+  },
+  "kills": [],
+  "tick": 115
+}