FeedFeedback fixes

[gaearon]

• 3cc4716: Lower the time threshold to 1500ms as discussed with @whyrusleeping.
• 14f00d5: Replies were missing feedContext because the parent item (which was unshifted) didn't have it. For our purposes, the entire convo has the same context. The fix is mostly copypaste from how we handle source. There's probably a simpler way to write this but I don't understand the data structure for sure — and this will definitely work.

Test Plan

Read the code for the first change. For the second change, added

--- a/src/state/queries/post-feed.ts
+++ b/src/state/queries/post-feed.ts
@@ -294,6 +294,14 @@ export function usePostFeedQuery(
                           AppBskyFeedPost.validateRecord(item.post.record)
                             .success
                         ) {
+                          let before = item.feedContext
+                          let after =
+                            i === 0 && slice.feedContext
+                              ? slice.feedContext
+                              : item.feedContext
+                          if (before !== after) {
+                            console.log('before != after', before, after)
+                          }

and verified that the log shows up for replies

[render]

Your Render PR Server URL is https://social-app-pr-3968.onrender.com.

Follow its progress at https://dashboard.render.com/web/srv-covsg30l6cac73av0i90.

[github-actions]

Old size	New size	Diff
7.14 MB	7.14 MB	149 B (0.00%)

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[pfrazee]

Yep looks good. I went for a simpler feedContext fallback (don't need to pay attention to the i===0 for this)