chore(rust): bump pinned toolchain to 1.99.1 (#126)

Weekly check found a newer stable Rust release.

`rust-toolchain.toml` is now pinned to `1.99.1`. The
normal CI checks run on this PR like any other — if the new toolchain
introduces
clippy/rustdoc/test failures, push fixes to this branch before merging
so the bump
and its fixes land together.

Author: jpage-godaddy

rust-toolchain.toml

@@ -1,3 +1,3 @@
 [toolchain]
-channel = "1.99.0"
+channel = "1.99.1"
 components = ["clippy", "rustfmt"]