feat(Popup): allow override of default config

Before we did not allow the default config to be overridden, but now we
do.

doc/libmodal-lua.txt

@@ -386,13 +386,20 @@ FUNCTIONS                                         *libmodal-lua-Popup-functions*
 		{keepBuffer}  A `boolean` that (when `true`) indicates the underlying
 		              |scratch-buffer| should be kept
 
-`self`:open()                                          *libmodal-lua-Popup.open()*
+`self`:open({config})                                  *libmodal-lua-Popup.open()*
 
 	Open the |Popup.window|.
 
 	Note: if the |Popup.window| is already open, then it will be reopened in
 	      case the |current_tabpage| has changed.
 
+	      In this case, it will also override the default options with the
+	      options in the window so there is no need to pass in {config} a
+	      second time.
+
+	Parameters: ~
+		{config}  Same as |nvim_open_win| {config}.
+
 `self`:refresh({inputBytes})                        *libmodal-lua-Popup.refresh()*
 
 	Update the content of the `Popup` using an array-like `table` of

lua/libmodal/src/collections/Popup.lua

@@ -81,8 +81,8 @@ end
 	* If the popup was already open, close it and re-open it.
 ]]
 --------------------------
-function _metaPopup:open()
-	local config = Popup.config
+function _metaPopup:open(config)
+	if not config then config = Popup.config end
 
 	if valid(self.window) then
 		config = vim.tbl_extend('force', config, api.nvim_win_get_config(self.window))