Modernize macos alias for Node.js 24

[jozefizso]

Summary

• bump the package to @appdmg/macos-alias@3.0.0 for the Node.js >=24 support floor
• keep CommonJS package exports and restore CommonJS tests for the first-stage contract
• replace Mocha/Standard/fs-temp test tooling with AVA and Node built-in temp-directory APIs
• update nan to the current patch line and keep it as the native boundary dependency
• refresh the Node 24 macOS/Linux workflow with Node 24-based GitHub Actions
• document platform behavior, native build requirements, and non-macOS volume-name behavior

Verification

• npm ci
• npm test
• npm audit --audit-level=moderate
• npm ls --omit=dev --all
• npm pack --dry-run
• node --check index.js
• node --check lib/create.js
• node --check lib/decode.js
• node --check lib/encode.js
• node --check lib/is-alias.js
• node --check test/basics.js
• node --check test/addon.js

Refs #21