Consider dropping support for Node.js <18.17.0

[wojtekmaj]

Hi! 👋

I’d like to propose raising the minimum supported Node.js version to ≥18.17.0.

Motivation:

• Dependency health: which@^5 requires Node ≥18.17.0. Today cross-spawn still supports Node ≥8, which effectively pins the tree to which@2 (released ~6 years ago). Bumping the engines field would unlock which@5 and similar modern updates.
  Maintenance & security: Supporting very old Node versions increases maintenance burden and limits the ability to adopt upstream fixes and ecosystem improvements.
• Modernization: Dropping legacy Node versions makes it easier to simplify code paths and align with the current ecosystem.

Compatibility / migration path:

• Projects still on legacy Node versions can continue using cross-spawn@7.
• For active LTS and current users (Node 18/20/22+), this change should be a no-op aside from receiving newer dependency versions.

Happy to open a PR with the engines bump, dependency updates, and CI matrix adjustments if this direction sounds good.

What do you think?