chore: replace coveralls with coveralls-next

[bjnewman]

Summary

• Replace deprecated coveralls package with coveralls-next

Why

The coveralls package depends on the deprecated request library and is no longer maintained. coveralls-next is a maintained fork that:

• Replaces request with native fetch
• Provides the same CLI interface (no script changes needed)
• Has fewer dependencies

See: https://github.com/nickmerwin/node-coveralls ("🚫 This repo is no longer maintained")

Testing

• npm run test:node passes
• coveralls binary still available via coveralls-next