downgrade to 1.81.0

Rust 1.81.0 introduces some interesting breaking changes for wasm
codegen and I'd rather not deal with those now.

See the compatibility notes section of
https://github.com/rust-lang/rust/releases/tag/1.82.0.

Author: Stebalien

rust-toolchain.toml

@@ -1,4 +1,4 @@
 [toolchain]
-channel = "1.82.0"
+channel = "1.81.0"
 components = ["clippy", "llvm-tools-preview", "rustfmt"]
 targets = ["wasm32-unknown-unknown"]