feat(indexer): dead-letter queue for events that repeatedly fail to persist - #549

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11, actions/setup-python@82c7e631bb3cdc910f68e0081d67478d79c6982d. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/