ldk: how to best convert a channel from cln to ldk

[vincenzopalazzo]

          (@vincenzopalazzo suggested to leave a comment so he can recall some stuff later https://discord.com/channels/@me/1244713070765539481/1276450545351000074)

It's important to understand how these values are used in core lightning, how they are set in graph, so we can know what we're doing is correct.
https://github.com/ElementsProject/lightning/blob/master/common/gossmap.c#L525

Originally posted by @raehat in #29 (comment)