feat: update character assets and registry for multiple packs

- Added new character images in .webp format for Dragon Ball FighterZ, Rivals of Aether II, and Skullgirls: 2nd Encore.
- Removed outdated .png images for characters in Dragon Ball FighterZ and Rivals of Aether II.
- Updated registry.json to reflect changes in character counts and total sizes for packs.
- Introduced new packs for BlazBlue Centralfiction and Rivals of Aether II with their respective assets and manifest files.
- Added scripts for updating image sizes and renaming images to match character slugs.

2xko/manifest.json

@@ -13,6 +13,7 @@
   "characters": [
     {"name": "Ahri", "slug": "ahri", "dlc": false, "sizeBytes": 482750},
     {"name": "Akali", "slug": "akali", "dlc": false, "sizeBytes": 458958},
+    {"name": "Blitzcrank", "slug": "blitzcrank", "dlc": false, "sizeBytes": 571047},
     {"name": "Braum", "slug": "braum", "dlc": false, "sizeBytes": 798568},
     {"name": "Caitlyn", "slug": "caitlyn", "dlc": false, "sizeBytes": 379717},
     {"name": "Darius", "slug": "darius", "dlc": false, "sizeBytes": 517856},