v1.5.0 of onyxsdk_pen

This plugin integrates the Onyx Pen SDK into Flutter to improve e-ink responsiveness in drawing apps. Changelog excerpt: - Hack: Excluded the mmkv lib from onyxsdk_pen as suggested by Onyx. This should complete the 16KB page size support to meet Google Play requirements. - Added support for Flutter 3.44 and migrated to the built-in Kotlin Gradle Plugin. This package now requires Flutter 3.44 or later.