autocargo and getdeps fixes

Summary:
Fix some issues with rust/shed that are causing problems with the getdeps builds.

Specifically:
- Disable autoexamples for `quickcheck_arbitrary_derive` as they clash with the manually defined example.
- Fix the fbcode_builder path for fb303.
- Fix import in `buffered_weight` memory bound code by avoiding use of `anyhow::Ok`.
- Fix unused item warnings in non-linux builds.
- Upgrade the version of proc-macro-crate that non-buck builds use to one that is available in the vendored packages.
- Fix documentation in sampling and bounded_traversal.

Reviewed By: RajivTS

Differential Revision: D78992994

fbshipit-source-id: cc19878b5ae8ed7cbd884805849be797a96d3fba

Author: markbt

build/fbcode_builder/manifests/fb303

@@ -11,7 +11,7 @@ repo_url = https://github.com/facebook/fb303.git
 cargo_config_file = source/fb303/thrift/.cargo/config.toml
 
 [crate.pathmap]
-fb303_core = fb303/thrift
+fb303_core = fb303/thrift/rust
 
 [build]
 builder = cmake