fix: parse comments in .nvmrc files

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Description

Fixes #1119.

getNodeVersionFromFile() already handles a full-line comment followed by a version in many cases, but some valid .nvmrc comment forms are still parsed as part of the Node version. In particular, a comment-only # line can be selected as the version, and inline comments or trailing whitespace can leave an invalid version string.

This change applies .nvmrc-specific preprocessing before the existing version matcher:

• remove # comments
• trim and discard blank lines
• return null when the file contains only comments or whitespace

The behavior of .tool-versions, JSON package files, and Volta configuration is unchanged. Thanks to @sodic for documenting the failing cases in #1119.

The committed dist/setup and dist/cache-save bundles were rebuilt from the updated source.

Validation

• npm run pre-checkin
• npm run format-check
• npm run lint
• npm test — 11 suites and 235 tests passed
• git diff --check