build: pin Rust toolchain version via rust-toolchain.toml

[23prime]

Checklist

• Target branch is main
• Status checks are passing

Summary

Closes #125

Reason for change

Rust had no pinned version in this repo (not managed via mise, and no rust-toolchain.toml), so a stale local rustup stable channel could drift below what dependencies require. This broke mise run rs-check locally with:

error: rustc 1.93.0 is not supported by the following packages:
  serial_test@4.0.1 requires rustc 1.93.1
  serial_test_derive@4.0.1 requires rustc 1.93.1

Changes

• Add rust-toolchain.toml pinning channel = "1.98.0" with components = ["rustfmt", "clippy"]
• Remove the now-redundant components: rustfmt, clippy input from check-rust.yml's setup-rust-toolchain step, since it now picks up components from the toolchain file

Notes

None

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository YAML (base), Organization UI (inherited)

Review profile: CHILL

Plan: Pro

Run ID: 83820ed1-accf-48c7-9a32-3d278e86e7c4

📥 Commits

Reviewing files that changed from the base of the PR and between cb74af9 and b27b12a.

📒 Files selected for processing (3)

• .github/workflows/check-markdown.yml
• .github/workflows/check-rust.yml
• rust-toolchain.toml

💤 Files with no reviewable changes (1)

• .github/workflows/check-rust.yml

Included review availability: 3 reviews are currently available. Your included PR review attempts over the past 7 days set your current allowance at 5 reviews per hour.

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📝 Walkthrough

Walkthrough

The repository pins Rust to version 1.98.0 with rustfmt and clippy. The Rust workflow relies on this configuration. The Markdown workflow installs Node.js with markdownlint-cli2.

Changes

Toolchain and CI setup

Layer / File(s)	Summary
Pin the Rust toolchain rust-toolchain.toml	The repository selects Rust 1.98.0 and enables the rustfmt and clippy components.
Align workflow installations .github/workflows/check-rust.yml, .github/workflows/check-markdown.yml	The Rust workflow removes explicit component installation. The Markdown workflow installs Node.js with markdownlint-cli2.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to b27b1

The PR pins the Rust toolchain and aligns the related checks with that pin. No actionable merge-blocking risk remains beyond normal checks and review.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Out of Scope Changes check	⚠️ Warning	The check-markdown.yml Node.js installation change is unrelated to the Rust requirements in issue #125.	Remove the unrelated check-markdown.yml change or link an issue that requires the Node.js installation update.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The Rust changes satisfy issue #125 by adding the pinned toolchain and required rustfmt and clippy components.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0 files. (2 skipped: 2 unsupported.)
Description check	✅ Passed	The description explains the Rust toolchain pin, component configuration, CI change, and reason for the change.
Title check	✅ Passed	The title clearly and concisely describes the main change: pinning the Rust toolchain with rust-toolchain.toml.

✨ Finishing Touches

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch feature/125-pin-rust-toolchain-version

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