Saturated publish fairness

[Indy2222]

Rumqttc disables the default features of the flume dependency, which in turn disables its eventual-fairness feature flag. Therefore, I believe that when the maximum number of in-flight messages is reached, all publishing tasks start to race, and message ordering can become biased due to hard-to-predict factors (e.g., the OS thread scheduler). I suggest enabling the eventual-fairness feature flag to address this.

The dependency:

rumqtt/rumqttc/Cargo.toml

Line 32 in c03ba8b

flume = { version = "0.11", default-features = false, features = ["async"] }

Flume feature flags:

https://github.com/zesterer/flume?tab=readme-ov-file#cargo-features