replace math/rand with math/rand/v2

[catatsuy]

This pull request includes several changes to update the math/rand package to math/rand/v2 and to replace the deprecated rand.Intn function with the new rand.IntN function across multiple files.

Package Update and Function Replacement:

• bench/asset/asset.go: Updated import from math/rand to math/rand/v2 and replaced rand.Intn with rand.IntN in multiple functions, including GetRandomActiveSellerIDs, GetRandomBuyerIDs, GetRandomImageFileName, GetRandomRootCategory, GetRandomChildCategory, GetRandomChildCategoryByParentID, and GenText. [1] [2] [3] [4] [5]
• bench/scenario/campaign.go: Updated import from math/rand to math/rand/v2 and replaced rand.Intn with rand.IntN in the popularListing function. [1] [2]
• bench/scenario/normal.go: Updated import from math/rand to math/rand/v2.
• bench/server/shipment.go: Updated import from math/rand to math/rand/v2 and replaced rand.Intn with rand.IntN in the Set method of the shipmentStore struct. [1] [2]