update deps; remove esp-idf-sys and embassy-net; make async-io optional

This innocent-starting PR unfortunately ended up with a bigger change surface than what I originally thought. Please take a look. If necessary, I can (try to) split.

Here, a summary of the changes. I've only listed these crates, whose update/removal ended up in (significant) code changes:

heapless 0.7 -> 0.8

(We still also use a version of heapless 0.7 because domain (the library our built-in mDNS uses) still needs it. But not for long, I hope.)

The biggest change in heapless 0.8 that affects us is that it it no longer implements From<&str> for heapless::String<N>. Instead, it implements TryFrom<&str> for heapless::String<N> (i.e. now returns an error rather than panicking if the &str is too big to fit in the heapless::String instance).

domain 0.7 -> 0.9

This was one of the two big changes (the removal of embassy-net described below being the other). The new domain API had changed significantly, so a lot of the code in the built-in mDNS responder had to be touched. Should work OK after the changes though, as I've already done this change a month ago for edge-mdns (which is more or less a replica of our built-in mDNS provider).

crypto-bigint 0.4 -> 0.5

Small API change in the reduce function (now called rem(-ainder))

Retired: `embassy-net` (+ `smoltcp`)

We used to have built-in support for using the baremetal UDP stack of embassy-net and smoltcp, under the embassy-net feature. This support is no longer necessary, as we can finally introduce the UdpSend and UdpReceive pair of async traits since Rust 1.75 (as I just did!). On the other hand, embassy-net and smoltcp bump their versions quite often (and are at 0.x still), so I don't see the point of maintaining the UDP mapping for these in rs-matter.

Implementing UdpSend and UdpReceive is not really necessary to do in rs-matter, as the user can do it outside, and it should be 10-20 lines of code, similarly to how we still do this for the STD async-io crate here.

As a result of the introduction of UdpSend and UdpReceive, we no longer need the Pipe utility, which was removed, nor the rs_matter::transport::udp module, which was also removed (the UDP traits are in rs_matter::transport::network now).

Made optional: `async-io`

async-io is one way to spin an async UDP stack on top of Rust STD. I cannot completely retire the async-io dependency from the rs-matter crate, as we need something to run our example. Yet, it is now optional, because users might prefer to use other async STD crates for the UDP stack. Namely, tokio.

Unlike embassy-net, async-io is now stable, at version 2.X, so keep it as an optional dependency even if we only need it for the examples is probably OK.

Retired: `esp-idf-sys` (for ESP IDF)

ESP IDF in Rust is a STD environment. Folks using ESP IDF with Rust should just use async-io (or tokio) for a UDP stack. During the last year, the explicit support for ESP IDF was upstreamed in both async-io V2 (and the smol echosystem as a whole), and in tokio V1.X.

ESP IDF still needs some "hand-holding" for multicast subscriptions (in mDNS) but this is due to upstream bugs that I need to address, and we better not workaround those anymore in rs-matter.

Example

I've removed the ESP-IDF specific parts from the example for now. I do realize we do need some examples on MCUs - not just with ESP IDF, but also baremetal ESP32. And other MCUs - like this example. But probably that needs to wait until we have an infrastructure similar to the C++ Matter SDK for running examples for various boards, rather than hacking support for all possible MCUs in a single example.

Update: `no-std-net`

The no-std-net crate is no longer actively developed. Moreover, its version 0.6 (the latest one) is not even compatible with STD. But we use it because we need the inet types in no_std.

Fortunately, the Rust STD inet types (SocketAddr, IpAddr and so on) will be available in Rust core as well, starting from Rust 1.77.

So in a couple of months we will remove this dependency as well.

project-chip / rs-matter