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`.
402f3bc934