try to fix server-side crashes

src/main/java/net/fretux/skillengine/client/ClientSkillEngineBridge.java

@@ -0,0 +1,43 @@
+package net.fretux.skillengine.client;
+
+import net.minecraft.resources.ResourceLocation;
+
+public final class ClientSkillEngineBridge {
+
+    private ClientSkillEngineBridge() {}
+
+    public static boolean clientHasSkill(ResourceLocation id) {
+        return SkilltreeClientState.isUnlocked(id);
+    }
+
+    public static int clientGetAbilitySlot(ResourceLocation id) {
+        return SkilltreeClientState.getSlotOfAbility(id);
+    }
+
+    public static ResourceLocation[] clientGetAbilitySlots() {
+        return SkilltreeClientState.getAbilitySlots();
+    }
+
+    public static void handleNodeUnlocked(ResourceLocation id, int newSkillPoints, boolean isAbility) {
+        if (isAbility) {
+            SkilltreeClientState.unlockAbility(id);
+        } else {
+            SkilltreeClientState.unlockNode(id);
+        }
+        SkilltreeClientState.setCurrentSkillPoints(newSkillPoints);
+    }
+
+    public static void handleSkillsSync(Iterable<ResourceLocation> unlocked,
+                                        Iterable<ResourceLocation> unlockedAbilities,
+                                        int skillPoints,
+                                        ResourceLocation[] abilitySlots) {
+        SkilltreeClientState.setUnlocked(unlocked);
+        SkilltreeClientState.setUnlockedAbilities(unlockedAbilities);
+        SkilltreeClientState.setCurrentSkillPoints(skillPoints);
+        SkilltreeClientState.setAbilitySlots(abilitySlots);
+    }
+
+    public static void handleCooldownSync(int slot, int cooldown) {
+        SkilltreeClientState.updateCooldown(slot, cooldown);
+    }
+}

src/main/java/net/fretux/skillengine/client/SkilltreeClientState.java

@@ -38,14 +38,18 @@ public class SkilltreeClientState {
         return unlocked.contains(id);
     }
 
-    public static void setUnlocked(Set<ResourceLocation> ids) {
+    public static void setUnlocked(Iterable<ResourceLocation> ids) {
         unlocked.clear();
-        unlocked.addAll(ids);
+        for (ResourceLocation id : ids) {
+            unlocked.add(id);
+        }
     }
 
-    public static void setUnlockedAbilities(Set<ResourceLocation> abilities) {
+    public static void setUnlockedAbilities(Iterable<ResourceLocation> abilities) {
         unlockedAbilities.clear();
-        unlockedAbilities.addAll(abilities);
+        for (ResourceLocation ability : abilities) {
+            unlockedAbilities.add(ability);
+        }
     }
 
     public static void setCurrentSkillPoints(int points) {
@@ -92,4 +96,4 @@ public class SkilltreeClientState {
     public static ResourceLocation[] getAbilitySlots() {
         return Arrays.copyOf(abilitySlots, abilitySlots.length);
     }
-}
+}