Refactor array handling in DotNet code generation

Introduces a ToEnumerable extension method to unify array and enumerable conversions in generated .NET code. Updates code generation logic to use ToEnumerable for array properties, simplifying and improving type safety. Also adds necessary using statement for Extensions in generated model files.

Author: Fellmonkey

src/SDK/Language/DotNet.php

@@ -512,10 +512,8 @@ public function getFunctions(): array
                     $subSchema = \ucfirst($property['sub_schema']);
 
                     if ($property['type'] === 'array') {
-                        $arraySource = $required
-                            ? "((IEnumerable<object>){$mapAccess})"
-                            : "({$v} as IEnumerable<object>)?";
-                        return "{$arraySource}.Select(it => {$subSchema}.From(map: (Dictionary<string, object>)it)).ToList()";
+                        $src = $required ? $mapAccess : $v;
+                        return "{$src}.ToEnumerable().Select(it => {$subSchema}.From(map: (Dictionary<string, object>)it)).ToList()";
                     } else {
                         if ($required) {
                             return "{$subSchema}.From(map: (Dictionary<string, object>){$mapAccess})";
@@ -539,9 +537,6 @@ public function getFunctions(): array
                 if ($property['type'] === 'array') {
                     $itemsType = $property['items']['type'] ?? 'object';
                     $src = $required ? $mapAccess : $v;
-                    $arraySource = $required
-                        ? "((IEnumerable<object>){$src})"
-                        : "({$src} as IEnumerable<object>)?";
 
                     $selectExpression = match ($itemsType) {
                         'string' => 'x.ToString()',
@@ -551,7 +546,7 @@ public function getFunctions(): array
                         default => 'x'
                     };
 
-                    return "{$arraySource}.Select(x => {$selectExpression}).ToList()";
+                    return "{$src}.ToEnumerable().Select(x => {$selectExpression}).ToList()";
                 }
 
                 // Handle integer/number

templates/dotnet/Package/Extensions/Extensions.cs.twig

@@ -12,6 +12,17 @@ namespace {{ spec.title | caseUcfirst }}.Extensions
             return JsonSerializer.Serialize(dict, Client.SerializerOptions);
         }
 
+        public static IEnumerable<object> ToEnumerable(this object value)
+        {
+            return value switch
+            {
+                object[] array => array,
+                IEnumerable<object> enumerable => enumerable,
+                IEnumerable nonGeneric => nonGeneric.Cast<object>(),
+                _ => throw new InvalidCastException($"Cannot convert {value?.GetType().Name ?? "null"} to IEnumerable<object>")
+            };
+        }
+
         public static string ToQueryString(this Dictionary<string, object?> parameters)
         {
             var query = new List<string>();

templates/dotnet/Package/Models/Model.cs.twig

@@ -7,6 +7,7 @@ using System.Text.Json.Serialization;
 {% if definition.properties | filter(p => p.enum) | length > 0 %}
 using {{ spec.title | caseUcfirst }}.Enums;
 {% endif %}
+using {{ spec.title | caseUcfirst }}.Extensions;
 
 namespace {{ spec.title | caseUcfirst }}.Models
 {