## Summary
* Upgrade the rust toolchain to 1.85.0. This does not increase the MSRV.
* Update windows trampoline to 1.86 nightly beta (previously in 1.85
nightly beta).
## Test Plan
Existing tests
## Summary
A lot of good new lints, and most importantly, error stabilizations. I
tried to find a few usages of the new stabilizations, but I'm sure there
are more.
IIUC, this _does_ require bumping our MSRV.
## Summary
Updates default toolchain to
[1.79](https://blog.rust-lang.org/2024/06/13/Rust-1.79.0.html).
There didn't seem to be any breaking changes besides xwin now requiring
lld llvm linker.
## Test Plan
Existing tests.
The `async fn` and return-position `impl Trait` in traits improve
`BuildContext` ergonomics. The traits use `impl Future` over `async fn`
to make the send bound explicit
(https://blog.rust-lang.org/2023/12/21/async-fn-rpit-in-traits.html).
The remaining changes are due to clippy.
