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/rip.go

@@ -124,8 +124,8 @@ func (g *RogueGame) totalWinner() {
 			obj.Flags.Set(Known)
 		case KindArmor:
 			worth = it.Armors[obj.Which].Worth
-			worth += (9 - obj.Arm) * 100
-			worth += 10 * (aClass[obj.Which] - obj.Arm)
+			worth += (9 - obj.ArmorClass) * 100
+			worth += 10 * (aClass[obj.Which] - obj.ArmorClass)
 			obj.Flags.Set(Known)
 		case KindScroll:
 			op := &it.Scrolls[obj.Which]
@@ -146,8 +146,8 @@ func (g *RogueGame) totalWinner() {
 			worth = op.Worth
 			if obj.RingKind() == RingAddStrength || obj.RingKind() == RingIncreaseDamage ||
 				obj.RingKind() == RingProtection || obj.RingKind() == RingDexterity {
-				if obj.Arm > 0 {
-					worth += obj.Arm * 100
+				if obj.Bonus > 0 {
+					worth += obj.Bonus * 100
 				} else {
 					worth = 10
 				}
@@ -160,7 +160,7 @@ func (g *RogueGame) totalWinner() {
 		case KindWand:
 			op := &it.Sticks[obj.Which]
 			worth = op.Worth
-			worth += 20 * obj.Charges()
+			worth += 20 * obj.Charges
 			if !obj.Flags.Has(Known) {
 				worth /= 2
 			}