Fix quadratic slowdown when ingesting data with uniform time (#3088)

### What
* Closes #3086
* Closes #433

This should also overall just speed up data insertion for the common
case of already-sorted data

### Checklist
* [x] I have read and agree to [Contributor
Guide](https://github.com/rerun-io/rerun/blob/main/CONTRIBUTING.md) and
the [Code of
Conduct](https://github.com/rerun-io/rerun/blob/main/CODE_OF_CONDUCT.md)
* [x] I've included a screenshot or gif (if applicable)
* [x] I have tested [demo.rerun.io](https://demo.rerun.io/pr/3088) (if
applicable)

- [PR Build Summary](https://build.rerun.io/pr/3088)
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Author: emilk

crates/re_arrow_store/src/store_write.rs

@@ -380,15 +380,21 @@ impl IndexedTable {
                 }
             }
 
-            debug!(
-                kind = "insert",
-                timeline = %timeline.name(),
-                time = timeline.typ().format(time),
-                entity = %ent_path,
-                len_limit = config.indexed_bucket_num_rows,
-                len, len_overflow,
-                "couldn't split indexed bucket, proceeding to ignore limits"
+            let bucket_time_range = bucket.inner.read().time_range;
+
+            re_log::debug_once!(
+                "Failed to split bucket on timeline {}",
+                bucket.timeline.format_time_range(&bucket_time_range)
             );
+
+            if bucket_time_range.min == bucket_time_range.max {
+                re_log::warn_once!(
+                    "Found over {} rows with the same timepoint {:?}={} - perhaps you forgot to update or remove the timeline?",
+                    config.indexed_bucket_num_rows,
+                    bucket.timeline.name(),
+                    bucket.timeline.typ().format(bucket_time_range.min)
+                );
+            }
         }
 
         trace!(
@@ -437,6 +443,13 @@ impl IndexedBucket {
         } = &mut *inner;
 
         // append time to primary column and update time range appropriately
+
+        if let Some(last_time) = col_time.last() {
+            if time.as_i64() < *last_time {
+                *is_sorted = false;
+            }
+        }
+
         col_time.push(time.as_i64());
         *time_range = TimeRange::new(time_range.min.min(time), time_range.max.max(time));
         size_bytes_added += time.as_i64().total_size_bytes();
@@ -495,9 +508,6 @@ impl IndexedBucket {
             }
         }
 
-        // TODO(#433): re_datastore: properly handle already sorted data during insertion
-        *is_sorted = false;
-
         *size_bytes += size_bytes_added;
 
         #[cfg(debug_assertions)]