optimizations + bugfixes

* Bombs explode on damage/explosion
* Orbits spell fixed
* Performance: implemented shared component indexes,
compiled Lua caching, and updates only for changed projectile fields.
Also removed accumulating hidden entity slots.

src/gun/projectiles.h

@@ -26,6 +26,7 @@ struct ProjDef {
     bool on_collision_die = true;
     int bounces_left = 0;                     // ProjectileComponent bounces_left: grenades bounce this often before they explode
     bool friendly_fire = false;               // ProjectileComponent.friendly_fire: hurts the herd of the shooter too
+    bool orbiting = false;                    // orbit_projectile: attached hazards can hit their caster after launch grace
     bool dont_hit_player = false;             // dont_hit_player: never hurts the player, whatever the herds
     int collide_with_shooter_frames = 0;      // the shooter itself is not hit during the first frames
     // HitEffectComponent (of the projectile and of its extra entities): what a hit does to the victim
@@ -53,7 +54,7 @@ struct ProjDef {
     bool die_on_liquid = false;               // die_on_liquid_collision
     float liquid_drag = 1.0f;                 // VelocityComponent liquid_drag (constructor default 1.0): the share of the speed lost per liquid cell around, per second
     bool displace_liquid = true;              // ProjectileComponent displace_liquid: the liquid around is pushed aside (the constructor default is not recovered, the explicit values of the data are honoured)
-    bool physics = false;                     // a thrown physics body (bombs): bounces and rolls, explodes only when its fuse runs out
+    bool physics = false;                     // a thrown physics body (bombs): bounces and rolls; fuse expiry or damage can detonate it
     bool creature = false;                    // a cast creature (SUMMON_WANDGHOST's wand_ghost_player.xml: no ProjectileComponent, an AI): the host spawns it as a whole entity, the GPU projectile only carries it out of the wand
     float break_speed = 0;                    // a breakable thrown body (SUMMON_EGG's egg_monster.xml: PhysicsBodyCollisionDamage + DamageModel + ExplodeOnDamage): an impact faster than this (px/s) kills it and it explodes with the ExplodeOnDamage config
     bool explode_on_death = false;
@@ -147,6 +148,8 @@ public:
     const ProjDef* def(const std::string& file);
     // A definition built from an entity description that is not a file (the runtime copy of a projectile after the scripts changed it), stored under `key`.
     const ProjDef* def_from(const std::string& key, const EntityDef& entity, const std::string& extras = "");   // + the extra entities of the shot (emitters, light, hit effects, homing)
+    // Stable identity for a script's projectile definition; host scheduling state is per instance.
+    static std::string script_definition_key(const EntityDef& entity);
     EntityDb& db() { return db_; }
     // The projectile with the extra entities a shot carries (c.extra_entities, comma separated): their particle emitters and light are added.
     const ProjDef* def(const std::string& file, const std::string& extras);