fix: handle edge object in serialization tests

Add `typecheck` script to package.json, expand tsconfig include
paths to cover tests and examples, and update serialization tests
to correctly resolve player IDs from relationship edges.

test/serialization.test.ts

@@ -277,7 +277,9 @@ describe("Serialization — complex state", () => {
       const comps = snap.entities[id];
       return comps.position && comps.velocity && !comps.health;
     })!;
-    const playerId = snap.relationships.ownedBy[bulletId];
+    const playerEdge = snap.relationships.ownedBy[bulletId];
+    const playerId =
+      typeof playerEdge === "string" ? playerEdge : playerEdge.target;
 
     // Player should have a name
     const playerComps = snap.entities[playerId];