feat: support loading extreamly large files

- Allocate initial file and leaf data outside of Buffer.arena
- Disable gutter diffs for very large files
- Disable syntax highlighting for very large files

src/tui/editor_gutter.zig

@@ -300,6 +300,10 @@ fn mouse_click_button5(_: *Self) error{Exit}!bool {
 }
 
 fn diff_update(self: *Self) !void {
+    if (self.lines > root.max_diff_lines) {
+        self.diff_symbols_clear();
+        return;
+    }
     const editor = self.editor;
     const new = if (editor.get_current_root()) |new| new else return;
     const old = if (editor.buffer) |buffer| if (buffer.last_save) |old| old else return else return;