Raise local version of Rust to 1.74.0

Ideally we would keep this at the MSRV but rust-analyzer now doesn't
work with anything older than this version. We had to jump up to 1.70
to get `block_box` to run the benchmarks anyways.

Author: the-mikedavis

rust-toolchain.toml

@@ -1,3 +1,3 @@
 [toolchain]
-channel = "1.70.0"
+channel = "1.74.0"
 components = ["rustfmt", "rust-src", "llvm-tools-preview"]