chore(deps): replace futures with futures-util & futures-executor

[negezor]

As the title says, this replaces the direct dependency on the entire features crate in favor of a smaller futures-util. This change removes 4 dependencies from the dependency tree.

[antifuchs]

That clippy failure is on me (need to update the main branch), will try to fix that & have you rebase if that's ok (:

[antifuchs]

master branch should be free from that clippy failure - would you mind merging it in or rebasing on top of it?