chore: bump nixpkgs + add cargo-expand to rust-build-inputs

[thedavidmeister]

nixpkgs bump brings wasm-bindgen-cli from 0.2.114 to 0.2.117 (highest available in current nixpkgs).

cargo-expand added to rust-build-inputs so macrotest-based test suites (rain.wasm) work without each consumer building cargo-expand from source.

Unblocks rainlanguage/rain.wasm#40.

Summary by CodeRabbit

• Chores
  • Updated development environment tooling to include the Cargo Expand utility for Rust workflows.
• Tests
  • Added an automated dev-shell test to verify the Cargo Expand command is available in the environment.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 54d17c77-a2e9-4d75-bb31-9382f0b67cfd

📥 Commits

Reviewing files that changed from the base of the PR and between 710dbeb and f3de711.

📒 Files selected for processing (2)

• flake.nix
• test/bats/devshell/rust-shell/cargo-expand.test.bats

✅ Files skipped from review due to trivial changes (1)

• test/bats/devshell/rust-shell/cargo-expand.test.bats

---

📝 Walkthrough

Walkthrough

Adds pkgs.cargo-expand to rust-build-inputs, updates packages.rust-shell-test to run a new Bats test, and adds rust-build-inputs to additionalBuildInputs so cargo expand is available and verified in the devshell.

Changes

Rust Build Inputs Expansion

Layer / File(s)	Summary
Add cargo-expand to Rust build inputs flake.nix	The rust-build-inputs exported attribute now includes pkgs.cargo-expand.
Test and wiring: verify cargo-expand in devshell test/bats/devshell/rust-shell/cargo-expand.test.bats, flake.nix	New Bats test runs cargo expand --version; packages.rust-shell-test runs this test and sets additionalBuildInputs to [ pkgs.bats ] ++ rust-build-inputs.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

"I nibble on code and hop with glee,
cargo-expand now follows me.
A test that hums, a version seen,
devshell ready, tidy and clean.
🐰✨"

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately reflects the main changes: bumping nixpkgs and adding cargo-expand to rust-build-inputs, which aligns with the PR objectives and file modifications.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch 2026-05-12-bump-nixpkgs-and-add-cargo-expand

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}