Shadow refactoring and improvements (#1959)

* Make shadow a type-only concept

* Prevent unnecessary init state recalc

* Use derived state instead of effects

* Batch emitter updates

* Use object first seen time instead of dataUpdatedAt

* Stop threading dataUpdatedAt through

* Use same value consistently

src/view/com/posts/Feed.tsx

@@ -76,7 +76,6 @@ let Feed = ({
   const opts = React.useMemo(() => ({enabled}), [enabled])
   const {
     data,
-    dataUpdatedAt,
     isFetching,
     isFetched,
     isError,
@@ -200,7 +199,6 @@ let Feed = ({
       return (
         <FeedSlice
           slice={item}
-          dataUpdatedAt={dataUpdatedAt}
           // we check for this before creating the feedItems array
           moderationOpts={moderationOpts!}
         />
@@ -208,7 +206,6 @@ let Feed = ({
     },
     [
       feed,
-      dataUpdatedAt,
       error,
       onPressTryAgain,
       onPressRetryLoadMore,

src/view/com/posts/FeedItem.tsx

@@ -40,7 +40,6 @@ export function FeedItem({
   record,
   reason,
   moderation,
-  dataUpdatedAt,
   isThreadChild,
   isThreadLastChild,
   isThreadParent,
@@ -49,12 +48,11 @@ export function FeedItem({
   record: AppBskyFeedPost.Record
   reason: AppBskyFeedDefs.ReasonRepost | ReasonFeedSource | undefined
   moderation: PostModeration
-  dataUpdatedAt: number
   isThreadChild?: boolean
   isThreadLastChild?: boolean
   isThreadParent?: boolean
 }) {
-  const postShadowed = usePostShadow(post, dataUpdatedAt)
+  const postShadowed = usePostShadow(post)
   const richText = useMemo(
     () =>
       new RichTextAPI({

src/view/com/posts/FeedSlice.tsx

@@ -11,12 +11,10 @@ import {makeProfileLink} from 'lib/routes/links'
 
 let FeedSlice = ({
   slice,
-  dataUpdatedAt,
   ignoreFilterFor,
   moderationOpts,
 }: {
   slice: FeedPostSlice
-  dataUpdatedAt: number
   ignoreFilterFor?: string
   moderationOpts: ModerationOpts
 }): React.ReactNode => {
@@ -44,7 +42,6 @@ let FeedSlice = ({
           record={slice.items[0].record}
           reason={slice.items[0].reason}
           moderation={moderations[0]}
-          dataUpdatedAt={dataUpdatedAt}
           isThreadParent={isThreadParentAt(slice.items, 0)}
           isThreadChild={isThreadChildAt(slice.items, 0)}
         />
@@ -54,7 +51,6 @@ let FeedSlice = ({
           record={slice.items[1].record}
           reason={slice.items[1].reason}
           moderation={moderations[1]}
-          dataUpdatedAt={dataUpdatedAt}
           isThreadParent={isThreadParentAt(slice.items, 1)}
           isThreadChild={isThreadChildAt(slice.items, 1)}
         />
@@ -65,7 +61,6 @@ let FeedSlice = ({
           record={slice.items[last].record}
           reason={slice.items[last].reason}
           moderation={moderations[last]}
-          dataUpdatedAt={dataUpdatedAt}
           isThreadParent={isThreadParentAt(slice.items, last)}
           isThreadChild={isThreadChildAt(slice.items, last)}
           isThreadLastChild
@@ -83,7 +78,6 @@ let FeedSlice = ({
           record={slice.items[i].record}
           reason={slice.items[i].reason}
           moderation={moderations[i]}
-          dataUpdatedAt={dataUpdatedAt}
           isThreadParent={isThreadParentAt(slice.items, i)}
           isThreadChild={isThreadChildAt(slice.items, i)}
           isThreadLastChild={