[ilnmtlbnm]

Summary

• GitHub runners ship rustup, which reads rust-toolchain.toml (channel, targets, components) on the first cargo/rustc call. This repo's rust-toolchain.toml already pins the channel and declares the targets/components the workflow needs, so pinning the toolchain a second time via the dtolnay/rust-toolchain action step is redundant and is the only place the Rust version would need bumping twice.
• Replaces the dtolnay/rust-toolchain@1.99.0 step with rustup show active-toolchain, which installs (and logs) the toolchain from rust-toolchain.toml on first use. Rust version bumps now happen in rust-toolchain.toml alone.

Test plan

• Could not run GitHub Actions before merge; pushing this branch alone does not trigger the workflow (push: is limited to branches: [main]). Opening this PR triggers the workflow via its pull_request: branches: [main] trigger — see the checks on this PR.