chore: remove destroy() methods from RenderTarget and SwapChain (these need to be managed by Viewer to handle instances where the viewer itself has been disposed

thermion_dart/lib/src/viewer/src/shared_types/render_target.dart

@@ -1,3 +1,3 @@
 abstract class RenderTarget {
-  Future destroy();
+  
 }

thermion_dart/lib/src/viewer/src/shared_types/swap_chain.dart

@@ -1,3 +1,3 @@
 abstract class SwapChain {
-  Future destroy();
+  
 }