Upgrade to tokio v1.0

[kim]

Reminder that tokio v0.3.0 introduces cancellable JoinHandles, which would obsolete SpawnAbortable.

Other changes may or may not be compatible, and may or may not be immediate improvements.

[geigerzaehler]

Since tokio v1 has been released we want to upgrade to that version.

[FintanH]

Depends on #1463 I believe.

[kim]

Is there a good grasp on how much would break if upstream moved to tokio 1?

It looks like quinn merged their migration -- while link doesn't care much about tokio 1, that patch also includes moving to rustls 0.19, which we would benefit from (we need to use the exact same version of rustls as quinn). It is also that this was a major blocker for quinn to make a new official release, and it would be good to be able to move away from the pinned git dependency.

Due to the breaking nature of this migration, the question is how we want to coordinate it? Do we want to wait until #1463 lands, then make a coordinated effort to move both projects to tokio 1, then proceed with net/next? Or is it a small enough change to conflate it with either next or net/next?

[FintanH]

Or is it a small enough change to conflate it with either next or net/next?

I could do a quick check on #1463 to see how much the compiler complains