Optimize VirtualizedList

Checkpoint optimizing virtualized list

Fixes for fallback rendering where terminalBuffer=false
Change terminalBuffer false back to the default while we fix performance
with very large chats.

Checkpoint changes to virtualized list.

Fix virtualized list

NO commit

Update ink version.

Fix UI snapshot mismatch in MainContent tests and VirtualizedList computation

Checkpoint.

docs/reference/configuration.md

@@ -376,6 +376,12 @@ their corresponding top-level category object in your `settings.json` file.
   - **Default:** `true`
   - **Requires restart:** Yes
 
+- **`ui.maxScrollbackLength`** (number):
+  - **Description:** Maximum number of lines to keep in the terminal scrollback
+    buffer.
+  - **Default:** `1000`
+  - **Requires restart:** Yes
+
 - **`ui.showSpinner`** (boolean):
   - **Description:** Show the spinner during operations.
   - **Default:** `true`