tsconfig.json (include): Whitelist files to build

This ended up being necessary because the distdir was being considered and
resulting in duplicate symbols.

tsconfig.json

@@ -15,6 +15,10 @@
         "node_modules/*",
         "src/types/*",
       ],
-    },
-  }
+    }
+  },
+  "include": [
+      "src/**/*",
+      "test/**/*"
+  ]
 }