They still need to be public for some reason, even
though they don't seem to be in input or output arguments.

Instead it can just be a generic parameter for methods that take a Behaviour<C, S>
argument, is tidier.

Some unnecessary members are no longer exported, and some docs improved.

This updates to latest git embassy deps (soon to be published on
crates.io).

The two nightly rust features are no longer required. Async Fn in Traits
has been merged.

Type Alias Impl Trait isn't in stable yet, so uses of singleton!() need
to be replaced with more cumbersome StaticCell. Eventually that can be
reverted.

There are also some small API changes to embassy and embedded-io crates
that needed fixing.

https://github.com/rust-embedded/cortex-m/discussions/503
-z is 229kB, -s is 248KB text, so worth keeping -z

Only KEX packets are allowed during KEX.
First packet must be kexinit when strict-kex
is negotiated

Includes updating some embassy versions, takepipe needed restructuring
to use split(). Takepipe isn't tested yet

Required updating embedded-io-async too

Also update to latest cyw firmware

Some picow menu improvements

Bump embassy version, embassy-net-tuntap is now its own crate
Also fix some warnings

Fix path for "size" of target in ci

Add sshwire::ssh_write_vec() helper

Wasn't being saved to flash before

Untested

A few other bits of tidying too

Also various extra tracing

Moved cyw43 git revision to top level Cargo.toml

embassy demos go back into the workspace, seems to work OK for the time
being.

Added toplevel Cargo.lock

Fixes embassy/demos/common CI

update other deps

Instead we set a flag in MethodPubkey which is the only use case for it.

Split verify() into ed25519 and rsa specific functions