chore: bump MSRV to 1.81.0

Author: zoedberg

.github/workflows/build.yml

@@ -65,7 +65,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        toolchain: [ nightly, beta, stable, 1.80.0 ]
+        toolchain: [ nightly, beta, stable, 1.81.0 ]
     steps:
       - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@master