Method SaveAsync(IEnumerable<IRedbObject>, IRedbUser)

🚀 BATCH SAVE with explicit user
Supports two strategy modes:

DeleteInsert: delete ALL values → BulkInsert/BulkUpdate of objects → BulkInsert of values
ChangeTracking: tree-based diff → two-phase EF SaveChanges

public Task<List<long>> SaveAsync(IEnumerable<IRedbObject> objects, IRedbUser user)