chore(deps): update dependency knip to v6

Author: renovate[bot]

bun.lock

@@ -49,7 +49,7 @@
     "@types/node": "25.5.0",
     "@vitest/coverage-v8": "4.1.2",
     "arktype": "2.2.0",
-    "knip": "5.88.1",
+    "knip": "6.0.6",
     "syncpack": "14.2.1",
     "tsdown": "0.21.5",
     "typescript": "5.9.3",