Un-overload Object fields and pre-parse damage dice (refactor step 3)

Object.Arm carried four meanings in C (o_arm/o_charges/o_goldval plus
ring bonuses); it is now four fields: ArmorClass, Charges, GoldValue,
and Bonus. Stats.Arm becomes Stats.ArmorClass. The Charges()/GoldVal()
accessor pair is gone.

Damage dice strings ("1x4/1x2") are parsed once into DiceSpec — at
table definition for the bestiary and weapon tables, at creation for
items — instead of re-parsed with atoi on every swing as fight.c
roll_em did. ParseDice preserves the C parse semantics exactly,
including the junk-tolerant "%%%x0" bestiary placeholder and the
"000x0" flytrap reset (regression-tested in dice_test.go); the
flytrap's growing grip becomes DiceSpec{{VfHit, 1}}.

Save format bumps to 5.4.4-go3 (field renames and retypes would
silently zero under gob's match-by-name decoding).

No behavior change; full suite green.

game/sticks.go

@@ -16,7 +16,7 @@ func (g *RogueGame) doZap() {
 		g.msg("you can't zap with that!")
 		return
 	}
-	if obj.Charges() == 0 {
+	if obj.Charges == 0 {
 		g.msg("nothing happens")
 		return
 	}
@@ -111,7 +111,7 @@ func (g *RogueGame) doZap() {
 		g.Items.Sticks[WandMagicMissile].Know = true
 		bolt := newObject()
 		bolt.Kind = KindGold // C set o_type='*': draws a '*' and is not a weapon
-		bolt.HurlDmg = "1x4"
+		bolt.HurlDmg = dice("1x4")
 		bolt.HPlus = 100
 		bolt.DPlus = 1
 		bolt.Flags = Missile
@@ -167,7 +167,7 @@ func (g *RogueGame) doZap() {
 		g.Items.Sticks[obj.Which].Know = true
 	case WandNothing:
 	}
-	obj.SetCharges(obj.Charges() - 1)
+	obj.Charges--
 }
 
 // drain does the drain-hit-points-from-player schtick (sticks.c drain).
@@ -213,7 +213,7 @@ func (g *RogueGame) fireBolt(start Coord, dir *Coord, name string) {
 	bolt := newObject()
 	bolt.Kind = KindWeapon
 	bolt.Which = int(WeaponFlame)
-	bolt.HurlDmg = "6x6"
+	bolt.HurlDmg = dice("6x6")
 	bolt.HPlus = 100
 	bolt.DPlus = 0
 	g.Items.Weapons[WeaponFlame].Name = name
@@ -322,17 +322,17 @@ func (g *RogueGame) fireBolt(start Coord, dir *Coord, name string) {
 // fixStick sets up a new wand or staff (sticks.c fix_stick).
 func (g *RogueGame) fixStick(cur *Object) {
 	if g.Items.WandType[cur.Which] == "staff" {
-		cur.Damage = "2x3"
+		cur.Damage = dice("2x3")
 	} else {
-		cur.Damage = "1x1"
+		cur.Damage = dice("1x1")
 	}
-	cur.HurlDmg = "1x1"
+	cur.HurlDmg = dice("1x1")
 
 	switch cur.WandKind() {
 	case WandLight:
-		cur.SetCharges(g.rnd(10) + 10)
+		cur.Charges = g.rnd(10) + 10
 	default:
-		cur.SetCharges(g.rnd(5) + 3)
+		cur.Charges = g.rnd(5) + 3
 	}
 }
 
@@ -343,7 +343,7 @@ func chargeStr(g *RogueGame, obj *Object) string {
 		return ""
 	}
 	if g.Options.Terse {
-		return fmt.Sprintf(" [%d]", obj.Charges())
+		return fmt.Sprintf(" [%d]", obj.Charges)
 	}
-	return fmt.Sprintf(" [%d charges]", obj.Charges())
+	return fmt.Sprintf(" [%d charges]", obj.Charges)
 }