Circe-Lagmon sends CTCP requests which are confusing for other clients/cause notifications about circe

[wasamasa]

If circe-lagmon.el were changed to use the existing PING/PONG commands for this purpose (or more realistically, if a new Circe module were written that implements the lagmon functionality using PING/PONG), I'd expect this issue to disappear. One concern against doing things this way was raised in #6:

• The IRC RFC does not guarantee that when sending an extra argument with the PING/PONG command, the corresponding response command would also include that extra argument. However, according to https://modern.ircdocs.horse/#ping-message this can actually be relied upon (not too surprisingly since it's been more than 10 years since the linked GitHub issue!). In the case a server does not implement it, lag detection can still be disabled.

That leaves actually implementing this. My IRC knowledge regarding the protocol itself is limited. Help is welcome.