feat: added node nightly version support #1419

[EwenSellitto]

Problem

The support for node@nightly version was missing. (as discussed in #1419 )

Solution

• Add node@nightly support: resolve against the Node nightly index, error only on unsupported custom
  tags, and download from the nightly base URL.
• Detect nightly builds via pre-release naming and use /download/nightly for fetches.
• Allow nightly as a version-like tag in CLI parsing/help text.
• Cover with unit tests for nightly URL selection and CLI parsing.