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

[Thaodan]

I noticed when using Circe-Lagmon on connections that use a bouncer together with other clients they can be confused or cause spam.

Since other clients treat the CTCP requests from circe as literal like it would be requested by another user they cause spam, each time a CTCP requests is answered the cause a notification.

[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.