Can you add support for the GUI-unifier mod?
https://mods.factorio.com/mod/GUI_Unifyer
My quickbar is getting full :|

Just add a button via the mod-gui like

local mod_gui = require("mod-gui")

in your control.lua and add the button like

local function create_gui_button(player)
  local button_flow = mod_gui.get_button_flow(player)
  if not button_flow.calcui_gui_button then
    button_flow.add({
        type = "sprite-button",
        name = "calcui_gui_button",
        sprite = "sprite_calcui_calculator",
        tooltip = {"calculator-ui.title"}
    })
  end
end

Then register the events

script.on_init(function()
  for _, player in pairs(game.players) do
    create_gui_button(player)
  end
end)

script.on_configuration_changed(function()
  for _, player in pairs(game.players) do
    create_gui_button(player)
  end
end)

script.on_event(defines.events.on_player_created, function(event)
  create_gui_button(game.players[event.player_index])
end)

and in your on_gui_click() event add

if event_name == "calcui_gui_button" then
  toggle_calculator(player)
  return
end

This alone won't add it to the unifier mod but it enables the integration by the author. I will ask him to add the button and also to add a public function for create_icon_entry() so other mods can add their butttons easily. Thanks in advance.