Fix CS8601 in generated proto→command list mappings

Generated CommandServiceImpl.g.cs had warnings like:
    Slug = request.Slug?.ToList(),   // CS8601 if Slug is non-nullable List<T>

The ?. was over-defensive: proto3 repeated fields are emitted as
RepeatedField<T> in C# and are NEVER null. The conditional access
made the result List<T>? which then triggered CS8601 when assigned
to a non-nullable target on the command POCO.

Dropped ?. in 4 emission sites in GrpcGenerator.cs covering:
- Top-level primitive list mapping (line 872)
- Top-level Guid list mapping (line 861)
- Nested primitive list mapping in NestedPropertyAssignment (line 1083)
- Complex list .Select chain in GenerateComplexListMapping (line 974,
  conditional: kept ?. for value-type collections where source.Items is
  read off a possibly-null wrapper message)

Real fix in the generator instead of CS8601 NoWarn suppression in
consumer csprojs. Consumers can drop the suppression after bumping.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Svrnty.CQRS.Grpc.Generators/GrpcGenerator.cs

@@ -858,7 +858,8 @@ public class GrpcGenerator : IIncrementalGenerator
                     var constructorType = prop.FullyQualifiedType.TrimEnd('?');
                     return $"{indent}{prop.Name} = new {constructorType}({source}?.Items?.Select(x => System.Guid.Parse(x)).ToArray() ?? System.Array.Empty<System.Guid>()),";
                 }
-                return $"{indent}{prop.Name} = {source}?.Select(x => System.Guid.Parse(x)).ToList(),";
+                // proto repeated fields are never null — drop ?. to avoid CS8601 on assignment to non-nullable target
+                return $"{indent}{prop.Name} = {source}.Select(x => System.Guid.Parse(x)).ToList(),";
             }
             else if (prop.IsValueTypeCollection)
             {
@@ -869,7 +870,8 @@ public class GrpcGenerator : IIncrementalGenerator
             else
             {
                 // Primitive list: just ToList()
-                return $"{indent}{prop.Name} = {source}?.ToList(),";
+                // proto repeated fields are never null — drop ?. to avoid CS8601 on assignment to non-nullable target
+                return $"{indent}{prop.Name} = {source}.ToList(),";
             }
         }
 
@@ -969,7 +971,9 @@ public class GrpcGenerator : IIncrementalGenerator
         var sb = new StringBuilder();
         // For value type collections, the proto message has an Items field containing the repeated elements
         var itemsSource = prop.IsValueTypeCollection ? $"{source}?.Items" : source;
-        sb.AppendLine($"{indent}{prop.Name} = {itemsSource}?.Select(x => new {prop.ElementType}");
+        // Value-type wrapper messages can be null (?.Items needs ?.). Plain proto repeated is never null.
+        var selectAccess = prop.IsValueTypeCollection ? "?." : ".";
+        sb.AppendLine($"{indent}{prop.Name} = {itemsSource}{selectAccess}Select(x => new {prop.ElementType}");
         sb.AppendLine($"{indent}{{");
 
         foreach (var nestedProp in prop.ElementNestedProperties!)
@@ -1078,7 +1082,8 @@ public class GrpcGenerator : IIncrementalGenerator
                 var constructorType = prop.FullyQualifiedType.TrimEnd('?');
                 return $"{indent}{prop.Name} = new {constructorType}({source}?.ToArray() ?? System.Array.Empty<{prop.ElementType ?? "object"}>()),";
             }
-            return $"{indent}{prop.Name} = {source}?.ToList(),";
+            // proto repeated fields are never null — drop ?. to avoid CS8601
+            return $"{indent}{prop.Name} = {source}.ToList(),";
         }
 
         // Handle complex types