Add Terestallization mechanics

Add Terestallization mechanics; implement Stellar type; fix bug with held item weights

src/system/achv.ts

@@ -125,6 +125,9 @@ export const achvs = {
   TRANSFER_MAX_BATTLE_STAT: new Achv('Teamwork', 'Baton pass to another party member with at least one stat maxed out', 'stick', 20),
   MAX_FRIENDSHIP: new Achv('Friendmaxxing', 'Reach max friendship on a Pokémon', 'soothe_bell', 25),
   MEGA_EVOLVE: new Achv('Megamorph', 'Mega evolve a Pokémon', 'mega_bracelet', 50),
+  GIGANTAMAX: new Achv('Absolute Unit', 'Gigantamax a Pokémon', 'dynamax_band', 50),
+  TERASTALLIZE: new Achv('STAB Enthusiast', 'Terastallize a Pokémon', 'tera_orb', 25),
+  STELLAR_TERASTALLIZE: new Achv('The Hidden Type', 'Stellar Terastallize a Pokémon', 'stellar_tera_shard', 25).setSecret(true),
   SPLICE: new Achv('Infinite Fusion', 'Splice two Pokémon together with DNA Splicers', 'dna_splicers', 10),
   MINI_BLACK_HOLE: new ModifierAchv('A Hole Lot of Items', 'Acquire a Mini Black Hole', 'mini_black_hole', 25, modifier => modifier instanceof TurnHeldItemTransferModifier).setSecret(),
   CATCH_MYTHICAL: new Achv('Mythical', 'Catch a mythical Pokémon', 'strange_ball', 50).setSecret(),

src/system/game-data.ts

@@ -763,7 +763,7 @@ export class GameData {
     this.scene.executeWithSeedOffset(() => {
       const neutralNatures = [ Nature.HARDY, Nature.DOCILE, Nature.SERIOUS, Nature.BASHFUL, Nature.QUIRKY ];
       for (let s = 0; s < defaultStarters.length; s++)
-        defaultStarterNatures.push(Phaser.Math.RND.pick(neutralNatures));
+        defaultStarterNatures.push(Utils.randSeedItem(neutralNatures));
     }, 0, 'default');
 
     for (let ds = 0; ds < defaultStarters.length; ds++) {