clippy: workspace-level clippy configurations

[BugenZhao]

Currently, we add a lot of clippy attributes at the root of each crate. It would be possible for us to forget to keep all crates consistent.

https://github.com/singularity-data/risingwave/blob/a15b40a28e86db1bb4d5c9b35f7303249d8102fd/src/stream/src/lib.rs#L16-L27

We may add them as rustc flags at .cargo/config.toml. An example:

https://github.com/EmbarkStudios/rust-ecosystem/blob/main/lints.toml

[xxchan]

upstream issue rust-lang/cargo#5034 🙏

[xxchan]

I'm also hoping to use #![feature] at workspace level 🤪