v2.15.0-k2.4.21-3.0+neoforge

• fix automatic event subscriber crashes on zero-argument methods and duplicate registrations for mods with multiple entrypoints
• fix legacy mod instance lookup and loading context access
• forward Forge config loading and reloading events to the mod event bus
• improve loading errors for incompatible KotlinLangForge artifacts, invalid mod constructors, and invalid annotated event handlers
• preserve original exception causes in mod loading errors
• improve early KLF/KFF compatibility diagnostics, including a Preloading Tricks suggestion when callbacks cannot load
• build(deps): bump org.jetbrains.kotlin.jvm from 2.4.20 to 2.4.21