bug#63595: 30.0.50; ERC 5.6: Add buffer-list and nick-list modules

["J.P." <jp@neverwas.me>]

I'm unsure whether there's a regression present on HEAD affecting
erc-speedbar (now the `nickbar' module). I've been noticing the idle
timer only seems to run after user input has been received and dealt
with. IOW, updates don't occur if simply leaving the window open and
otherwise not interacting with Emacs. I suppose we could run the timer
function manually, like on `erc-post-insert-hook' (perhaps guarded by
some debouncing logic), but I'd only want to do so if we can confirm
this isn't a regression.