feat(sdk): Implement RoomEvents::reset, push_gap, replace_gap_at and events.

This patch implements the following wrapper methods (over
`LinkedChunk`): `push_gap`, `replace_gap_at` and `events`. This patch
also implements the `reset` method that clears/drops all chunks in the
`LinkedChunk`.

crates/matrix-sdk/src/event_cache/store.rs

@@ -230,6 +230,11 @@ impl RoomEvents {
         Self { chunks: LinkedChunk::new() }
     }
 
+    /// Clear all events.
+    pub fn reset(&mut self) {
+        self.chunks = LinkedChunk::new();
+    }
+
     /// Return the number of events.
     pub fn len(&self) -> usize {
         self.chunks.len()
@@ -251,6 +256,11 @@ impl RoomEvents {
         self.chunks.push_items_back(events)
     }
 
+    /// Push a gap after existing events.
+    pub fn push_gap(&mut self, gap: Gap) {
+        self.chunks.push_gap_back(gap)
+    }
+
     /// Insert events at a specified position.
     pub fn insert_events_at<I>(
         &mut self,
@@ -273,6 +283,22 @@ impl RoomEvents {
         self.chunks.insert_gap_at(gap, position)
     }
 
+    /// Replace the gap identified by `gap_identifier`, by events.
+    ///
+    /// Because the `gap_identifier` can represent non-gap chunk, this method
+    /// returns a `Result`.
+    pub fn replace_gap_at<I>(
+        &mut self,
+        items: I,
+        gap_identifier: ChunkIdentifier,
+    ) -> StdResult<(), LinkedChunkError>
+    where
+        I: IntoIterator<Item = SyncTimelineEvent>,
+        I::IntoIter: ExactSizeIterator,
+    {
+        self.chunks.replace_gap_at(items, gap_identifier)
+    }
+
     /// Search for a chunk, and return its identifier.
     pub fn chunk_identifier<'a, P>(&'a self, predicate: P) -> Option<ChunkIdentifier>
     where
@@ -328,6 +354,13 @@ impl RoomEvents {
         self.chunks.ritems()
     }
 
+    /// Iterate over the events, forward.
+    ///
+    /// The oldest event comes first.
+    pub fn events(&self) -> impl Iterator<Item = (ItemPosition, &SyncTimelineEvent)> {
+        self.chunks.items()
+    }
+
     /// Iterate over the events, starting from `position`, backward.
     pub fn revents_from(
         &self,