Add awaitNostr shim to prevent authentication issues

[melvincarvalho]

Currently, the nostr.chat application might encounter issues during the authentication process if the extension is not fully loaded before attempting to authenticate. This can result in errors or unexpected behavior in the app.
Proposed solution

To address this issue, I suggest we implement an awaitNostr shim that ensures the extension is completely loaded before proceeding with authentication. This can be achieved by wrapping the authentication function in a promise that resolves only when the extension has been loaded.