Blast API shutting down

Hey,

[Blast API](https://blastapi.io/) will shut down after October 31, 2025. In [your code here](https://github.com/5afe/react-native-passkeys-tutorial/blob/main/.env-sample#L14), you could replace it with a public endpoint from [ChainList](https://chainlist.org), or use [Chainstack](https://chainstack.com) for more reliable setups.