Adds support to the library for tokio 0.2 backward-compatibility. This should hopefully benefit, and prevent lavalink-rs from being blocked on this feature.
These can be reached using, e.g., `gateway-tokio-02`, `driver-tokio-02`, `serenity-rustls-tokio-02`, and `serenity-native-tokio-02` features.
Naturally, this requires some jiggering about with features and the underlying CI, which has been taken care of. Twilight can't be handled in this way, as their last tokio 0.2 version uses the deprecated Discord Gateway v6.
* Driver Benchmarks
Benchmarks driver use cases for single packet send,
multiple packet send, float vs opus, and the cost of
head-of-queue track removal.
Mix costs for large packet counts are also included.
This is a prelude to the optimisations discussed in
#21.
* Typo in benchmark
* Place Opus packet directly into packet buffer
Cleans up some other logic surrounding this, too. Gets a 16.9% perf improvement on opus packet passthrough (sub 5us here).
* Better track removal
In theory this should be faster, but it aint. Keeping in case
reducing struct sizes down the line magically makes this
faster.
* Reduce size of Input, TrackHandle
Metadata is now boxed away. Similarly, TrackHandles are neatly Arc'd to reduce their size to pointer length (and mitigate the impact of copies if we add in more fields).
