Spawn driver tasks implicitly

[Ralith]

We're already reliant on tokio's thread locals for UDP socket and timer registration, and Handle::enter provides adequate mechanism to route spawns to a particular runtime if absolutely needed, so passing driver tasks to the user explicitly wasn't buying us much considering how big a footgun it is.

[Ralith]

I'm fairly confident that this is the direction I'd like to go. Just need to update more tests and, at least ideally, find a way to test that the implicitly spawned tasks get cleaned up properly.

[djc]

Looks okay to me. I'll give it a full review once it's complete.

[Ralith]

Rebased onto #589 and #590, plus a couple additional bugfixes. I think this is ready now, modulo the dependency PRs being merged.

[Ralith]

Er, right, still need to port h3.

[github-actions]

Pull Request Test Coverage Report for Build 612d7479973aa2250e24254c65764344853adc0b-PR-586

• 1 of 19 (5.26%) changed or added relevant lines in 4 files are covered.
• 19 unchanged lines in 6 files lost coverage.
• Overall coverage decreased (-0.1%) to 70.536%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
quinn-h3/src/connection.rs	0	3	0.0%
quinn-h3/src/server.rs	0	5	0.0%
quinn-h3/src/client.rs	0	10	0.0%

Files with Coverage Reduction	New Missed Lines	%
quinn-proto/src/packet.rs	1	86.44%
quinn-h3/src/client.rs	2	0.0%
quinn-proto/src/shared.rs	3	47.67%
../../../../../usr/share/rust/.cargo/registry/src/github.com-1ecc6299db9ec823/tracing-futures-0.2.0/src/lib.rs	3	66.67%
quinn-h3/src/server.rs	4	0.0%
../../../../../usr/share/rust/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-channel-0.3.1/src/mpsc/mod.rs	6	78.34%

Totals
Change from base Build 29dfcab51f5000c1f553fb5b8a97a9a0758c9b1b:	-0.1%
Covered Lines:	9911
Relevant Lines:	14051

---

💛 - Coveralls

[Ralith]

Okay, now we're good. This is still missing checks that we're not leaking tasks, but I'm not sure if there's a good way to do that with tokio 0.2 yet.

[Ralith]

On consideration, I think I can refactor the whole connection setup path to be a lot more straightforward; going to try to get that in before merging.

[Ralith]

Okay, I think this is ready.

[Ralith]

Rebased.

[djc]

This needs one more rebase...

[stammw]

🎉