Keep spoil percent when serializing item stacks (#1096)

serialize_item_stack did not store the spoil percent and
deserialize_item_stack did not pass it to set_stack, so spoilable items
arrived fresh after a transfer. Store it when above 0 and restore it. The
percent is used instead of spoil_tick since tick counts differ between servers.

Co-authored-by: ILLISIS <jayson.harris01@gmail.com>
Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

packages/host/modules/clusterio/serialize.lua

@@ -17,6 +17,7 @@ end
 
 local has_create_grid = compat.version_ge("1.1.7")
 local has_quality = compat.version_ge("2.0.0")
+local has_spoilage = compat.version_ge("2.0.0")
 
 -- Equipment Grids are serialized into an array of equipment entries
 -- where ench entry is a table with the following fields:
@@ -106,6 +107,7 @@ end
 --	 c: count
 --	 q: quality (optional)
 --	 h: health (optional)
+--	 p: spoil percent (optional)
 --	 d: durability (optional)
 --	 a: ammo count (optional)
 --	 l: label (optional)
@@ -139,6 +141,7 @@ function serialize.serialize_item_stack(slot, entry)
 	entry.c = slot.count
 	if has_quality and slot.quality.level ~= 0 then entry.q = slot.quality.name end
 	if slot.health < 1 then entry.h = slot.health end
+	if has_spoilage and slot.spoil_percent > 0 then entry.p = slot.spoil_percent end
 	if slot.type == "tool" and slot.durability then entry.d = slot.durability end
 	if slot.type == "ammo" then entry.a = slot.ammo end
 	if slot.is_item_with_label then
@@ -177,6 +180,7 @@ function serialize.deserialize_item_stack(slot, entry)
 	}
 	if entry.q then item_stack.quality = entry.q end
 	if entry.h then item_stack.health = entry.h end
+	if entry.p then item_stack.spoil_percent = entry.p end
 	if entry.d then item_stack.durability = entry.d end
 	if entry.a then item_stack.ammo = entry.a end