Remove wrangling since std types are just re-exports of core and alloc types whenever possible

[the10thWiz]

This also makes the std feature dependent on alloc.

I'm pretty sure serde has the import wrangling section simply so they can use crate::lib::*; in both the serialize and deserialize modules. My understanding is that import wrangling should never be needed.

Every std type with a corresponding core or alloc type is (to the best of my knowledge) actually just a re-export of the core or alloc type. For crates that don't need alloc or std only types, they can just declare #![no_std] unconditionally, and still work just fine with std crates.

[JRRudy1]

I knew that was the case for core vs. std, but wasn't sure if it worked the same way for alloc and didn't find any definitive answers after a quick google. I want to dig a little bit more just to make sure there aren't cases where importing from alloc prevents optimizations or anything, but your solution is much cleaner if all else is equal

[JRRudy1]

I read through std/lib.rs and std/prelude.rs and I'm convinced. Originally I wasn't positive whether the alloc crate is linked in differently or something, but you are totally right that it is just reexported. Thanks a lot for the review and edits, it definitely simplifies things 👍