chore: latest rainix + modernize CI

[thedavidmeister]

Brings rain.error onto the latest rainix and the modern reusable-workflow CI.

• flake: input rainprotocol/rainix → rainlanguage/rainix, lockfile regenerated to latest (current rust-overlay / rust 1.94.0). Dropped the unused self lambda arg (deadnix). nix develop -c cargo test passes (14 tests).
• CI: replaced the legacy rainix.yaml matrix with the rainix-rs.yaml@main reusable thin caller (rs-static + rs-test ubuntu/macos + rs-wasm + rs-wasm-test). The old matrix invoked rainix-rs-artifacts, which latest rainix no longer exposes.
• publish: replaced the manual publish.yml (cargo release) with package-release.yaml calling the rainix-autopublish.yaml@main reusable for rain-error-decoding — push-to-main, content-gated and race-safe (rainix#184/#186).
• gitignore the nix develop-generated .pre-commit-config.yaml.

🤖 Generated with Claude Code

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: 8ff4f0ba-82e0-4761-bfe5-198a0a193804

📥 Commits

Reviewing files that changed from the base of the PR and between 75b57f8 and d54cd89.

⛔ Files ignored due to path filters (1)

• flake.lock is excluded by !**/*.lock

📒 Files selected for processing (6)

• .github/workflows/package-release.yaml
• .github/workflows/publish.yml
• .github/workflows/rainix-rs.yaml
• .github/workflows/rainix.yaml
• .gitignore
• flake.nix

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch 2026-05-26-latest-rainix

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[github-actions]

@coderabbitai assess this PR size classification for the totality of the PR with the following criterias and report it in your comment:

S/M/L PR Classification Guidelines:

This guide helps classify merged pull requests by effort and complexity rather than just line count. The goal is to assess the difficulty and scope of changes after they have been completed.

Small (S)

Characteristics:

• Simple bug fixes, typos, or minor refactoring
• Single-purpose changes affecting 1-2 files
• Documentation updates
• Configuration tweaks
• Changes that require minimal context to review

Review Effort: Would have taken 5-10 minutes

Examples:

• Fix typo in variable name
• Update README with new instructions
• Adjust configuration values
• Simple one-line bug fixes
• Import statement cleanup

Medium (M)

Characteristics:

• Feature additions or enhancements
• Refactoring that touches multiple files but maintains existing behavior
• Breaking changes with backward compatibility
• Changes requiring some domain knowledge to review

Review Effort: Would have taken 15-30 minutes

Examples:

• Add new feature or component
• Refactor common utility functions
• Update dependencies with minor breaking changes
• Add new component with tests
• Performance optimizations
• More complex bug fixes

Large (L)

Characteristics:

• Major feature implementations
• Breaking changes or API redesigns
• Complex refactoring across multiple modules
• New architectural patterns or significant design changes
• Changes requiring deep context and multiple review rounds

Review Effort: Would have taken 45+ minutes

Examples:

• Complete new feature with frontend/backend changes
• Protocol upgrades or breaking changes
• Major architectural refactoring
• Framework or technology upgrades

Additional Factors to Consider

When deciding between sizes, also consider:

• Test coverage impact: More comprehensive test changes lean toward larger classification
• Risk level: Changes to critical systems bump up a size category
• Team familiarity: Novel patterns or technologies increase complexity

Notes:

• the assessment must be for the totality of the PR, that means comparing the base branch to the last commit of the PR
• the assessment output must be exactly one of: S, M or L (single-line comment) in format of: SIZE={S/M/L}
• do not include any additional text, only the size classification
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