ci: run quinn-udp tests with fast-apple-datapath

[mxinden]

I suggest we test the feature introduced in #1993 on CI.

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Related, we are currently integrating it into Neqo (mozilla/neqo#2302). On our localhost Download benchmark it shows ~10% throughput improvement.

[djc]

Ohh, beta ICEd in CI -- filed.

[gretchenfrage]

Would it make sense to only run it with this feature on macos, rather than both without and with?

[Ralith]

IIRC we're deliberately supporting both cases, since the fast path is a bit sketchy.

[gretchenfrage]

FWIW, the compiler bug also manifested from me rebasing #1912 over main. https://github.com/quinn-rs/quinn/actions/runs/12700393147/job/35402953810

[djc]

@Ralith did you want to review this?

[mxinden]

Would it make sense to only run it with this feature on macos, rather than both without and with?

IIRC we're deliberately supporting both cases, since the fast path is a bit sketchy.

Agreed. Long term we might be able to remove the not(fast-apple-datapath). But that needs rigorous testing of fast-apple-datapath first. Releasing this to Firefox Nightly will be a good first step.