feat: update async-std to 1.6.2

[dignifiedquire]

(still testing, will mark as ready when I am confident it is working)

Ref #1612

[dignifiedquire]

Ready for review, all tests are now passing out of the box, thanks to the diligent work from @stjepang

[mxinden]

This looks good to me. Thanks @dignifiedquire @stjepang for the help!

As I have not been very involved in #1588 I will leave it up to the rest to approve.

Its a bummer that we can't just ignore 1.6.0 and 1.6.1 (See rust-lang/cargo#5286), but given that 1.5.0 and 1.6.2 are within the same major version I doubt any downstream dependency would complain being forced to update.

[tomaka]

I'm trying this on Polkadot and it seems to work so far. 🚀

[tomaka]

I'm still going to test more, but I think it's ok to merge this.
I think we should wait for a couple days (during which a node will be running with this PR) to put it in a release of libp2p though.

[twittner]

Then we should wait with the merge until we have published the new libp2p version which will require async-std 1.5.0. If we merge this now we would use 1.6.2 as a lower bound.

[tomaka]

It's been running for 4 hours now, and there isn't any anomaly in sight.

[tomaka]

Still no anomaly, everything running smoothly.
Let's merge this?