Give item categories and subtypes real types (refactor step 2)

ObjectKind separates what an item is from how it draws: Object.Type
(a byte that doubled as the map character) becomes Kind ObjectKind,
with Glyph() producing the display character and objectKindForGlyph
converting back at the map boundary. KindWand covers the C 'stick'
category. The magic-missile bolt uses KindGold, matching C's literal
o_type='*' trick, with a comment.

PotionKind, ScrollKind, RingKind, WandKind, WeaponKind, ArmorKind and
TrapKind are now iota enums with Stringer (names come from the base
info tables); Object gains typed accessors (obj.RingKind(), ...) and
Launch is typed WeaponKind. beTrapped returns TrapKind. The
getItem/inventory/whatis prompt filters take ObjectKind, with
KindCallable/KindRingOrStick replacing the C CALLABLE/R_OR_S
sentinels; wizard.c's type_name table is subsumed by
ObjectKind.String(). IsRing/IsWearing/initWeapon/doPot signatures are
typed accordingly.

The save format version becomes 5.4.4-go2: the gob field rename would
otherwise silently zero Kind when reading old saves.

No behavior change; full suite green.

game/save.go

@@ -11,6 +11,11 @@ import (
 // what state.c's rs_fix_thing did: pointers that alias other structures
 // (equipment, chase targets, room membership) are encoded as indices.
 
+// saveFormatVersion identifies the snapshot layout; it changes whenever a
+// field rename or retype would make gob silently mis-decode an older
+// save ("go2": Object.Type became Kind ObjectKind).
+const saveFormatVersion = Release + "-go2"
+
 // destRef encodes a monster's chase target (state.c rs_write_thing's
 // (kind, index) pairs).
 type destRef struct {
@@ -165,7 +170,7 @@ func (g *RogueGame) packIdx(obj *Object) int {
 func (g *RogueGame) snapshot() *SaveState {
 	p := &g.Player
 	st := &SaveState{
-		Version:    Release,
+		Version:    saveFormatVersion,
 		Seed:       g.Rng.Seed,
 		Dnum:       g.Dnum,
 		Whoami:     g.Whoami,
@@ -530,7 +535,7 @@ func Restore(path string, cfg Config) (*RogueGame, error) {
 	if err := gob.NewDecoder(f).Decode(&st); err != nil {
 		return nil, fmt.Errorf("%s: corrupt or incompatible save file: %w", path, err)
 	}
-	if st.Version != Release {
+	if st.Version != saveFormatVersion {
 		return nil, fmt.Errorf("sorry, saved game is out of date")
 	}