make sure that fetching verification pubkeys does not delay message rendering

[tomholub]

Separately, it seems to me that the pgp block doesn't finish rendering anything until the decrypt -> try to verify -> aha missing pubkey -> fetch pubkeys -> reverify loop is complete.

I didn't investigate in detail, could it be true? I'd recommend to write a test as follows:

• add /attester/pub/this.pubkey.takes.long.time.to.load@sender.test to attester mock api. It will include a 5 second sleep before returning the pubkey.
• write a ui test that checks a message signed by that key
• wait in ui test of the pgp block for texts in this sequence: 1) message body 2) "verifying signature" 3) good signature

Do you have a similar test that checks for the "verifying signature" step specifically?

Originally posted by @tomholub in #4144 (comment)