Automatic toolchain upgrade to nightly-2025-08-09 (model-checking#4283)

Update Rust toolchain from nightly-2025-08-08 to nightly-2025-08-09
without any other source changes.

Co-authored-by: celinval <35149715+celinval@users.noreply.github.com>

Author: github-actions[bot]

rust-toolchain.toml

@@ -2,5 +2,5 @@
 # SPDX-License-Identifier: Apache-2.0 OR MIT
 
 [toolchain]
-channel = "nightly-2025-08-08"
+channel = "nightly-2025-08-09"
 components = ["llvm-tools", "rustc-dev", "rust-src", "rustfmt"]