refactor: address review nits

- merge gsapResizeIntercept's duplicate module imports
- move the core-constant imports to the file headers (picker, domEditingDom)
- justify the cross-realm HTMLElement casts (iframe-realm nodes fail
  instanceof; access is duck-typed)

packages/core/src/runtime/picker.ts

@@ -1,4 +1,5 @@
 import type { RuntimeJson, RuntimeOutboundMessage, RuntimePickerElementInfo } from "./types";
+import { COLOR_GRADING_SOURCE_HIDDEN_ATTR } from "../colorGrading";
 import { swallow } from "./diagnostics";
 
 type PickerModuleDeps = {
@@ -17,7 +18,6 @@ const PICKER_BLOCK_SELECTOR = [
   "[data-hyperframes-picker-block]",
   "[data-hyper-shader-loading]",
 ].join(",");
-import { COLOR_GRADING_SOURCE_HIDDEN_ATTR } from "../colorGrading";
 
 export type PickerModule = {
   enablePickMode: () => void;