Add weapon textures, refactor item spawning

src/items/InventoryItem.tscn

@@ -0,0 +1,24 @@
+[gd_scene load_steps=2 format=3 uid="uid://dme37m7q60um4"]
+
+[sub_resource type="BoxShape3D" id="BoxShape3D_84bq1"]
+size = Vector3(0.778381, 0.929947, 0.731567)
+
+[node name="InventoryItem" type="Node3D"]
+
+[node name="Pickup" type="Area3D" parent="."]
+unique_name_in_owner = true
+collision_layer = 0
+collision_mask = 4
+
+[node name="Sprite" type="Sprite3D" parent="Pickup"]
+unique_name_in_owner = true
+transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, -0.0322805, 0)
+pixel_size = 0.0003
+billboard = 2
+double_sided = false
+alpha_cut = 1
+texture_filter = 0
+
+[node name="CollisionShape3D" type="CollisionShape3D" parent="Pickup"]
+transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0.0600509, 0.26725, 0.180481)
+shape = SubResource("BoxShape3D_84bq1")