Fix duplicate class and annotation placement lint errors

Classes contributed to by more than one file now carry the `partial`
attribute. trains.lua declared its command as `ExpCommand_Artillery`,
which was a copy paste.

`Color.0` and `MapPosition.0` became `.struct` in fmtk 2.1.6.

emmylua rejects `@type` on a function statement or a `do` block, so
those are moved onto the local or replaced by `@param` and `@return`.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

exp_gui/module/control.lua

@@ -16,7 +16,7 @@ Storage.register(player_elements, function(tbl)
     player_elements = tbl
 end)
 
---- @class Gui
+--- @class (partial) Gui
 local Gui = {
     define = ExpElement.new,
     from_argument = ExpElement.from_argument,

exp_gui/module/elements.lua

@@ -1,4 +1,4 @@
---- @class Gui
+--- @class (partial) Gui
 local Gui = require("modules/exp_gui")
 
 --- @class Gui.elements

exp_gui/module/styles.lua

@@ -1,4 +1,4 @@
---- @class Gui
+--- @class (partial) Gui
 local Gui = require("modules/exp_gui")
 
 --- @class Gui.styles

exp_gui/module/toolbar.lua

@@ -1,5 +1,5 @@
 
---- @class Gui
+--- @class (partial) Gui
 local Gui = require("modules/exp_gui")
 local ExpElement = require("modules/exp_gui/prototype")
 local mod_gui = require("mod-gui")