Add Stream::process_uninit to accept &[MaybeUninit<u8>] output

[NobodyXu]

Having a safe API for MaybeUninit<u8> would be necessary for async-compression to wrap and reduce the performance penalty of initializing the buffer for all tokio::io::* traits implementation.

Also update process_vec API to use the new API instead of passing a &mut [u8] which technically violates rust's semantics.

Related PR: trifectatechfoundation/bzip2-rs#147 rust-lang/flate2-rs#502

[NobodyXu]

Removed unused std::slice import and apply cargo-fmt suggestion

[NobodyXu]

CI is green now

[ChanTsune]

@NobodyXu
Thank you for your PR!

Overall, the content looks fine, but there’s one point that concerns me.
It seems that process_uninit has no direct way of knowing the length written.
While it’s possible to calculate it by calling total_out before and after invoking process_uninit, in that case I believe the documentation should explicitly state this.
Alternatively, the return value should include the length written.

[NobodyXu]

Thanks, I've updated the doc for process_uninit.

I decided to keep API of process and process_uninit similar with minimum change so that users can transition to new API seemlessly

[ChanTsune]

Thank you for updating the documentation. I’ll merge it.

[ChanTsune]

@NobodyXu
Thank you for your contribution!

I’d love to include your name in the THANKS file. Do you have a preferred name you'd like us to use?

[NobodyXu]

I’d love to include your name in the THANKS file. Do you have a preferred name you'd like us to use?

My preferred name is Jiahao XU, thank you for reviewing my PR!