PDS's firehose can skip cursor values

[imax9000]

Describe the bug

When connecting to PDS's firehose with a previous cursor, it occasionally skips a few sequential cursor values without emitting #info message.

To Reproduce

Steps to reproduce the behavior:

1. Connect to wss://agaric.us-west.host.bsky.network/xrpc/com.atproto.sync.subscribeRepos?cursor=13892059 sometime within the next hour
2. Read seq field from the first received message

Expected behavior

13892060

Actual behavior

13892061

Additional context

Yes, I know that the spec does not say they have to be sequential. But they are in the current implementation, and I'm checking the increment to detect a reset when connecting to Relay's firehose, which does not emit #info at all, so there's no other way to know if there's a break in continuity.