feat(rules): encode arcane_caster and armor_spell_failure from the sheets

- arcane_caster true: misty (Magus/Bard sheet class), nairda (Witch/
  Sorcerer), thrune_agent (Human magus 8, KB bestiary/thrune-agent.md);
  lich already true. False: oni (Cleric), tammara (Gunslinger/
  Warpriest - divine), esha (Cavalier/Rogue, spell-like only), the
  companions harvie/ierlieth/jeanne/esha_mount and the remaining
  monsters.
- armor_spell_failure stays 0 everywhere, as the effective PF1e value:
  nairda and the lich wear no armor (sheet note "Pas d'armure", KB lich
  block); misty's mithral shirt (RAW ASF 10%, magic-items/mithral-shirt
  .md) and the thrune agent's +1 studded leather (15%) are light armor
  and every spell they cast is on their own class list - magus and bard
  cast their own spells in light armor with no arcane spell failure
  (classes/magus.md, classes/bard.md).
- tests/test_spell_failure.py: the lich/oni smoke test becomes a
  full-data table pinning all 15 combatants' flags with per-entry
  sources. No shipped combatant incurs a non-zero ASF; the failure roll
  itself stays covered by the synthetic armored-caster tests.

data/pcs/nairda.json

@@ -26,6 +26,8 @@
     "will": 7
   },
   "casting_ability": "int",
+  "arcane_caster": true,
+  "armor_spell_failure": 0,
   "spell_slots": {
     "1": 4,
     "2": 3