Tracking issue for reducing future sizes

[GnomedDev]

Serenity's future sizes are quite large, leading to clippy::large_futures warnings and suboptimal performance.

This is a list of known problems leading to these large futures.

• The Http interface is forced to keep builders in futures even after serializing them, due to the &impl serde::Serialize signature.
• Some functions take ownership of a type, then only use a couple fields even though it's carrying over an await point.
• • This probably requires enabling struct_lit_single_line in rustfmt settings.
• More to be found

[mkrasnitski]

What is the value of future-size-threshold that you set to produce warnings for you? Sticking with the default value produces none for me.

[GnomedDev]

The default, but my message event handler is tokio::joining 3 futures together all doing serenity stuff, which peaked at 19kb before #3357 and around 15k after.