Type vlayer forward declarations and config entries

The gui element locals are declared at the top and assigned far below,
so emmylua inferred them as nil at every use site.

circuit_oc was reassigned from a control behaviour to a logistic
section, which hid every section method behind the wrong type.

allowed_items entries carry heterogeneous optional properties, now
described by a class.

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

exp_legacy/module/config/vlayer.lua

@@ -35,6 +35,20 @@ return {
         storage_output = 1, -- >0 allows for item teleportation (allowed_items only)
     },
 
+    --- @class Vlayer.ItemProperties
+    --- @field starting_value number
+    --- @field required_area number
+    --- @field production number?
+    --- @field discharge number?
+    --- @field capacity number?
+    --- @field surface_area number?
+    --- @field fuel_value number?
+    --- @field power boolean?
+    --- @field modded boolean? Set when the item is registered from a modded equivalent
+    --- @field base_game_equivalent string?
+    --- @field multiplier number?
+
+    --- @type table<string, Vlayer.ItemProperties>
     allowed_items = { --- @setting allowed_items List of all items allowed in vlayer storage and their properties
         --[[
             Allowed properties: