This is more consistent with the way we use std::cmp over the
codebase and avoids `use std`, which is only actually needed to
support older rustcs, so feels a bit awkward.
This isn't a big difference in the API, but it avoids needing to
wrap a given NetworkGraph in a RwLock before passing it, which
makes it much easier to generate C bindings for.
This caused a bunch of cascading changes, including
passing loggers down to Channels in function calls
rather than having each Channel have a pointer to the
ChannelManager's Logger (which was a circular reference).
Other structs that the Channel had passed its Logger to also
had their loggers removed. Other newly unused Loggers were
also removed, especially when keeping them would've caused
a bunch of extra test changes to be necessary, e.g. with
the ChainWatchInterfaceUtil's Logger.
We need to always set lowest_inbound_channel_fees to None if there
are no channels (and we should ignore the channels which are
disabled for the purpose of lowest-fee calculations). Further, we
cannot unwrap the channel lookups as they may be for channels which
are not related to the channel we are processing an update for.
Finally, we can satisfy borrowck much easier since things are on
self instead of on a MutexGuard.
Because we expose the internals we don't need a method to log
their contents anymore, and get_addresses can now avoid copying as
we expose the RwLock directly
