fix!: require styled-components ^6.1, node >= 18

BREAKING CHANGE: This module now requires the peer dependency `styled-components` greater than or
equal to version 6.1. This aligns with Sanity v3.37.0 and higher.

BREAKING CHANGE: This module now requires Node.js 18 or higher.
This shouldn't really impact anyone beyond developers of the module, since this really only applies
to the build tooling.

Author: rexxars