1.6.0

• All DrawingViewState objects now adopt @Serializable annotation.
• Make DrawingViewState.isHistoryEmpty, DrawingViewState.isUndoneEmpty,
  DrawingViewState.numHistorySteps and DrawingViewState.numUndoneSteps public.
• bump Gradle plugin to 8.7.2, Kotlin to 2.0.20
• bump buildToolsVersion 35.0.0, targetSdkVersion, compileSdkVersion to 35

Full Changelog: 1.5.1...1.6.0