I'd like to add a minor improvement and some small bug fixes to this
feature (new in ERC 5.6). The improvement concerns the command
`erc-fill-wrap-cycle-visual-movement', which cycles through three
flavors of interactive movement: "logcial-line", "screen-line", and
"DWIM". In an unfortunate omission (by me), basic line-wise movement
commands weren't initially included. But now I'm thinking users would at
least appreciate being able to navigate by whole IRC message when the
logical-line variant (nil state) is active. That's what the third patch
does.

The second patch introduces a minor change involving the mostly
unrelated bug#60933, which did away with the oddball "nickname" entry in
`erc-button-alist' and introduced an escape hatch (in the
function-valued variable `erc-button-nickname-callback-function') for
those needing access to the excised entry's "on-click" callback. The
interface was initially defined to accommodate the nick-button's
"erc-data" object, in this case a list containing a lone arg, the
nickname, to pass to the callback. However, in this instance, we're not
really obliged to preserve compatibility because this is a new variable,
and the old hard-wired callback, `erc-nick-popup', remains untouched.

Therefore, I think we should take this opportunity to redefine this
interface to accept any number of TBD trailing args after the nickname.
This will make it easier to retain more informative data for rich UI
features without resorting to hacks, like hiding data in text-properties
of public strings, which can leak memory. I also think we ought to
deprecate this variable even though it's new in ERC 5.6 to stress the
fact that the default value is basically required when using ERC as an
interactive client.