chore: remove implicit tokio feature

[WaterWhisperer]

Fixes #511

Motivation

We have an implicit tokio Cargo feature because we don't use dep: syntax for it.

Solution

makes the tokio dependency explicit

[jplatte]

That CI error is really strange. Could you try moving the rust-toolchain action step in the MSRV job after the cargo update steps? Maybe this is an old bug in cargo that since got fixed.

[WaterWhisperer]

That CI error is really strange. Could you try moving the rust-toolchain action step in the MSRV job after the cargo update steps? Maybe this is an old bug in cargo that since got fixed.

Sure, thanks for the review

[jplatte]

Okay, so that didn't work. I have another idea: Can you (after rebasing, this PR seems to have a conflict now) move the toolchain action back, and also add --all-features to the problematic cargo update invocation? I think it's maybe saying that tokio is not a dependency that can be updated because it needs to resolve what dependencies actually exist and uses the default features for that unless told otherwise.

[WaterWhisperer]

Okay, so that didn't work. I have another idea: Can you (after rebasing, this PR seems to have a conflict now) move the toolchain action back, and also add --all-features to the problematic cargo update invocation? I think it's maybe saying that tokio is not a dependency that can be updated because it needs to resolve what dependencies actually exist and uses the default features for that unless told otherwise.

Seems that cargo update command does not support the --all-features flag.

[WaterWhisperer]

This error is really strange :(

[jplatte]

I'll try to reproduce / fix locally, when I get the time.