fix: pin Rust toolchain via rust-toolchain.toml, fix deprecated f64 path

docs/contributing/development.md

@@ -6,7 +6,7 @@
     Building on Linux and Windows requires compiling `rusty_v8` from source, which can take 30+ minutes and requires additional dependencies (Python, Clang/LLVM, etc.). See the [rusty_v8 build documentation](https://github.com/denoland/rusty_v8?tab=readme-ov-file#build-v8-from-source) for platform-specific requirements.
 
 - **Python**: 3.10 or higher
-- **Rust**: Latest stable toolchain (install via [rustup](https://rust-lang.org/tools/install/))
+- **Rust**: Install via [rustup](https://rust-lang.org/tools/install/); the version is pinned in `rust-toolchain.toml` and rustup selects it automatically, keeping local builds, lints, and CI on the same toolchain
 - **uv**: Fast Python package manager (install via [uv docs](https://docs.astral.sh/uv/getting-started/installation/))
 - **Make**: Build automation tool (usually pre-installed on macOS/Linux)
 

rust-toolchain.toml

@@ -0,0 +1,7 @@
+# Single source of truth for the Rust toolchain: rustup picks this up
+# automatically for local builds, CI, and the V8 archive builder containers,
+# so lint results (clippy -D warnings) stay reproducible everywhere.
+# Bump deliberately; `make all` must pass under the new version.
+[toolchain]
+channel = "1.99.0"
+components = ["clippy", "rustfmt"]

src/runtime/config.rs

@@ -498,7 +498,6 @@ impl RuntimeConfig {
 mod tests {
     use super::*;
     use pyo3::types::PyFloat;
-    use std::f64;
 
     #[test]
     fn test_default_config() {