Root: reduce transaction timeout to 50ms

The current value of 200ms is too long and makes river feel very slow
when it it hit due to an application being very slow/frozen.

The new timeout of 50ms seems to be rarely hit in practice even on
slower hardware such as my old Thinkpad x220. When it is hit the system
feels much more responsive than when the 200ms timeout is hitdespite the
guilty application window potentially being visible in the wrong
location/size a bit longer.

river/Root.zig

@@ -580,7 +580,7 @@ fn sendConfigures(root: *Self) void {
             root.inflight_configures,
         });
 
-        root.transaction_timeout.timerUpdate(200) catch {
+        root.transaction_timeout.timerUpdate(50) catch {
             std.log.scoped(.transaction).err("failed to update timer", .{});
             root.commitTransaction();
         };