Add tests to established connections

[tomaka]

Adds a test to the established connections.

I initially just wanted to write regression tests, unfortunately the first test I wrote doesn't pass because of this generally messy piece of code.
I'm going to fix that generally messy piece of code before we can merge this PR.

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Update:

Working on the tests revealed a couple of bugs that I've fixed.

Additionally, I've also made a change where we now pass a timeout to open_notifications_substream to allow configuring it and to make it similar to add_request.

[mergify]

Automatically approving tomaka's pull requests. This auto-approval will be removed once more maintainers are active.

[github-actions]

twiggy diff report

Difference in .wasm size before and after this pull request.

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 Delta Bytes │ Item
─────────────┼──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
      +10232 ┊ smoldot::libp2p::connection::established::substream::Substream<TNow,TRqUd,TNotifUd>::read_write2::h0f7e34003cbeb9ac
       -9740 ┊ smoldot::libp2p::connection::established::substream::Substream<TNow,TRqUd,TNotifUd>::read_write2::ha53af24fcae11d83
        -361 ┊ core::ptr::drop_in_place<smoldot::libp2p::connection::established::substream::SubstreamInner<smoldot_light_wasm::Instant,smoldot::libp2p::collection::SubstreamId,()>>::h1e3f9403be0e4678
        +361 ┊ core::ptr::drop_in_place<smoldot::libp2p::connection::established::substream::SubstreamInner<smoldot_light_wasm::Instant,smoldot::libp2p::collection::SubstreamId,()>>::h22e17444d1dc3c35
        -231 ┊ smoldot::libp2p::connection::established::single_stream::SingleStream<TNow,TRqUd,TNotifUd>::open_notifications_substream::h1b4c3657c0864ad0
        +221 ┊ smoldot::libp2p::connection::established::single_stream::SingleStream<TNow,TRqUd,TNotifUd>::open_notifications_substream::h1ac919ba1c2df275
        -112 ┊ data[0]
         +60 ┊ smoldot::libp2p::connection::established::single_stream::SingleStream<TNow,TRqUd,TNotifUd>::process_substream::h908acae52f8a1cf5
         -49 ┊ smoldot::libp2p::read_write::ReadWrite<TNow>::close_write_if_empty::hc16464fdb62e71a1
         -33 ┊ smoldot::libp2p::connection::yamux::Yamux<T>::remove_dead_substream::h7492aefbefdaed4a
         +18 ┊ smoldot::libp2p::collection::multi_stream::MultiStreamConnectionTask<TNow,TSubId>::substream_read_write::h2da2553fcea14137
         +15 ┊ smoldot::libp2p::connection::established::single_stream::SingleStream<TNow,TRqUd,TNotifUd>::read_write::h9f6718ead376aea4
         -15 ┊ type[68]: (i32, i32, i32, f64, i32, i32, i32, i32, i32, i32, i32, i32) -> nil
         +15 ┊ type[69]: (i32, i32, i32, f64, i32, i32, i32, i32, i32, i32, i32, i32) -> nil
         -12 ┊ type[103]: (i32, i32, i32, i32, i32, i32, i64, i64, i64) -> nil
         +12 ┊ type[104]: (i32, i32, i32, i32, i32, i32, i64, i64, i64) -> nil
         -12 ┊ type[79]: (i32, f64, i32, i32, i32, i64, i32, i32) -> i64
         +12 ┊ type[80]: (i32, f64, i32, i32, i32, i64, i32, i32) -> i64
         -12 ┊ type[81]: (i32, i32, f64, i32, i32, i32, i64, i64) -> i64
         +12 ┊ type[82]: (i32, i32, f64, i32, i32, i32, i64, i64) -> i64
         +24 ┊ ... and 79 more.
        +306 ┊ Σ [99 Total Rows]

[tomaka]

Tests are now passing. Will add more tests.

[tomaka]

This PR is definitely a bit embarrassing: it revealed many unimplemented things, which now are.