com.acutecoder.kmp.preference.PreferenceObserver.observers retains disposed KmpProjectPane

```
  207M        1 ROOT: Static field: com.acutecoder.kmp.preference.PreferenceObserver.observers
  207M        1 (root): java.util.ArrayList
  207M        1 elementData: java.lang.Object[]
  207M        7 []: com.acutecoder.kmp.projectview.KmpProjectPane$$Lambda+0x0000000801b10748
  207M        6 arg$1: com.acutecoder.kmp.projectview.KmpProjectPane (disposed)
```