Some dep crates are still always using defmt though, needs fixing.

This should let us ignore ZLP problems.
Perhaps performance could be improved later.

Allows ssh serial@picow to attach to the usb serial port

- takepipe needs better mutex handling, currently take() only
completes when the current user performs a read/write.

- Updated toolchain and cyw43

- Added context to demo Shell.

More async auth methods will probably follow

It's slow on the rp2040. Instead we should add entropy inside
the ed25519 signature generation.

Perhaps should have a different name, is mostly internal conveniences

A cutdown std program may only want ed25519

Is slightly more consistent

It isn't used and didn't seem to work with panic=abort experiments

- ServBehaviour::hostkeys() now returns a slice of references
  since we can't clone SignKeys and don't want to move
  them out of Config. May need rethinking.

- embassy demos common code is now a proper crate

- Updated various embassy deps

Fixes build failures. Toolchain is updated, but we can't upgrade to
latest nightly because it fails with an ICE, possibly
https://github.com/rust-lang/rust/issues/110206

thread 'rustc' panicked at 'DefId(35:311 ~ embedded_io[99f8]::asynch::Write::write::{opaque#0}) does not have a "def_span"', compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs:205:1

Also fix pubkey packet test and fix some doc formatting

Remove some unneeded messages, don't panic on TCP socket errors

Fixes hanging at the end of "git push"

This allows it to work when use for eg git

Requires alloc. Only tested with std.

Some other RAM reductions

We don't need OwnedSig state any more (we send straight away), simplify
packet creation.

sunsetc host -s sftp

would fail before. argh has a "greedy" attribute to handle that

Saves around 5kB in picow demo, functions can be shared between
EncodeBytes/EncodeLen/EncodeHash

Could eventually perhaps go behind a rsa feature

Instead of exiting

github.com disconnects immediately. OpenSSH and Dropbear clients
don't send it anyway.

sunsetc can now push itself to github!

Not perfect, it won't handle
-a option

etc after the hostname

Is now sufficient to run "sftp -S sunsetc"

The Behaviour makes a separate request for pty or shell etc once the
channel is established. This gets rid of InitReqs which wasted space.

Subsystem is also supported (not tested yet)