perf: Migrate vendor management gumps to DynamicGump/StaticGump (#2431)

## Summary
Converts `ReclaimVendorGump`, `VendorInventoryGump`, and the five gumps in `VendorRentalGumps.cs` from legacy `Gump` to `DynamicGump` / `StaticGump<T>` with the static `DisplayTo` entry-point pattern.

| Gump | Target | Reason |
|---|---|---|
| `ReclaimVendorGump` | DynamicGump | Variable vendor inventory list count. |
| `VendorInventoryGump` | DynamicGump | Variable inventory list; keeps `from` (per-row button depends on owner check). |
| `BaseVendorRentalGump` (abstract) → `VendorRentalContractGump`, `VendorRentalOfferGump`, `RenterVendorRentalGump`, `LandlordVendorRentalGump` | DynamicGump | Layout has many conditional sections driven by `GumpType` enum. |
| `VendorRentalRefundGump` | StaticGump | Fixed layout; vendor name, shop name, refund amount in `BuildStrings` placeholders. |

All builder labels and string slots use `$"{value}"` interpolated-string-handler form for zero-allocation text.

Updates callers in `PlayerMobile`, `HouseSign`, `RentedVendor`, and `VendorRentalContract`.

Projects/UOContent/Multis/Houses/HouseSign.cs

@@ -263,7 +263,7 @@ public partial class HouseSign : Item
             }
             else
             {
-                from.SendGump(new VendorInventoryGump(sign.Owner, from));
+                VendorInventoryGump.DisplayTo(from, sign.Owner);
             }
         }
     }