add some default types to de-duplicate similar implmentations

Pilz.Net/Api/Client/BaseChildItemClient.cs

@@ -0,0 +1,34 @@
+using Pilz.Net.Api.Messages;
+using Pilz.Net.Data;
+
+namespace Pilz.Net.Api.Client;
+
+public abstract class BaseChildItemClient<T>(IApiClient client) : BaseClient<T>(client), IBaseChildItemClient<T> where T : IDataObject
+{
+    public virtual async Task<IEnumerable<T>> GetAll(int parentId) 
+    {
+        return (await client.SendRequest<GeneralItemMessages<T>.Items>(ApiEndpoint, HttpMethod.Get, new ApiParameterCollection
+        {
+            ["parent"] = parentId,
+        })).EnsureOk().Items;
+    }
+
+    public override async Task<T> Save(T item)
+    {
+        if (item.Id == 0)
+            throw new NullReferenceException("Item has no parent yet!");
+        return await base.Save(item);
+    }
+
+    public virtual async Task<T> Save(T item, int parentId)
+    {
+        return (await client.SendRequest<GeneralItemMessages<T>.Item>(
+            ApiEndpoint,
+            HttpMethod.Post,
+            GenerateUpdateMessage(item, true),
+            new ApiParameterCollection
+            {
+                ["parent"] = parentId,
+            })).EnsureOk().Item;
+    }
+}