Update Cosmos API to 1.21.8, configure Altitude Nexus repository, and adjust ProgressBookOpener for incomplete quests

settings.gradle.kts

@@ -1,8 +1,18 @@
 rootProject.name = "AQuest"
 
+val nexusUser = providers.gradleProperty("alttdSnapshotUsername").orNull ?: System.getenv("NEXUS_USERNAME")
+val nexusPass = providers.gradleProperty("alttdSnapshotPassword").orNull ?: System.getenv("NEXUS_PASSWORD")
+
 dependencyResolutionManagement {
     repositories {
         mavenCentral()
+        maven {
+            url = uri("https://repo.alttd.com/repository/alttd-snapshot/")
+            credentials {
+                username = nexusUser
+                password = nexusPass
+            }
+        }
         maven("https://repo.destro.xyz/snapshots") // Altitude - Cosmos
         maven("https://jitpack.io") { // Vault
             content { includeGroup("com.github.milkbowl") }