feat(rules): scale healing spells with caster level

PF1e (SRD spells/cure-light-wounds.md): 'cures 1d8 points of damage +1
point per caster level (maximum +5)'; (spells/cure-moderate-wounds.md):
'cures 2d8 points of damage +1 point per caster level (maximum +10)'.
A HealEffect now carries the same DamageFlatScaling spec as damage
effects (S1b) and resolves it through effective_formula(caster_level)
at cast time, so the flat bonus grows with the caster and stops at the
stated cap. The engine passes the caster's level into _apply_heal_effect
(required keyword: no silent level-0 under-heal); Maximize Spell
maximizes the scaled formula. Cure Light/Moderate Wounds ship the SRD
values; inflict_light_wounds already carried its scaling_flat.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

data/spells/cure_moderate_wounds.json

@@ -9,8 +9,9 @@
   "effects": [
     {
       "type": "heal",
-      "formula": "2d8+3"
+      "formula": "2d8",
+      "scaling_flat": { "amount": 1, "per_levels": 1, "max": 10 }
     }
   ],
-  "description": "Cures 2d8+3 points of damage. Will save negates (harmless)."
+  "description": "Cures 2d8 points of damage +1 point per caster level (maximum +10). Will save negates (harmless)."
 }