stats property
If you are looking for precomputed values for the stats on a weapon, this is where they are stored. Technically these are the "Display" stat values. Please see DestinyStatsDefinition for what Display Stat Values means, it's a very long story... but essentially these are the closest values BNet can get to the item stats that you see in-game. These stats are keyed by the DestinyStatDefinition's hash identifier for the stat that's found on the item.
Implementation
@JsonKey(name:'stats')
Map<String, DestinyInventoryItemStatDefinition>? stats;