Allow doctors to trade without running out of space (#62677)

The Tacoma ranch doctor rapidly runs out of space when you are paying for operations. If they are given a shopkeeper item group, then they don't run out of space.

See #62673

data/json/npcs/classes.json

@@ -102,6 +102,7 @@
     "bonus_str": { "rng": [ -2, 0 ] },
     "bonus_int": { "rng": [ 0, 2 ] },
     "bonus_per": { "one_in": 4 },
+    "shopkeeper_item_group": "NC_DOCTOR_misc",
     "skills": [
       { "skill": "ALL", "level": { "mul": [ { "one_in": 3 }, { "sum": [ { "dice": [ 3, 2 ] }, { "rng": [ -1, -3 ] } ] } ] } },
       { "skill": "firstaid", "bonus": { "rng": [ 2, 6 ] } }