Previously, in each of our fuzz tests we had a dummy test which
had a hard-coded hex string which it passed into the fuzz target
so that when a failing test case was found, its hex could be
copied into the test and you could run cargo test to analyze the
failure. However, this was somewhat unwieldy as converting large
tests back and forth between hex and raw files is quite annoying.
Instead, we replace each of those tests with a test in each target
that looks for files in fuzz/test_cases and runs each file it finds.
Since we're editing every bin target anyway, we also automate adding
no_main to libfuzzer builds with #![cfg_attr].
Instead of having in-memory access to the list of private keys
associated with a channel, we should have a generic API which
allows us to request signing, allowing the user to store private
keys any way they like.
The first step is the (rather mechanical) process of templating
the entire tree of ChannelManager -> Channel impls by the
key-providing type. In a later commit we should expose only public
keys where possible.
