Generated factories fail to compile for init-only or required properties

[kgkoutis]

Problem

GetPropertiesToSet in DataFactoryWriter.cs treats every settable property the same way and emits a post-construction assignment:

var o = new T(...);
var o0 = provider.Resolve<...>(...);
if (o0.IsResolved)
{
    o.SomeProperty = o0.Value;
}

This doesn't compile when SomeProperty is:

• init-only ({ get; init; }) — CS8852, init-only properties can only be assigned in an object initializer.
• required — CS9035, required members must be assigned in the object initializer of the enclosing new expression (or via a constructor annotated [SetsRequiredMembers]).

Since GetPropertiesToSet only filters on GetMethod/SetMethod being non-null, it doesn't distinguish these from ordinary mutable properties, so any [DataFactory]-registered type using init or required members currently fails to compile.

Repro

[DataFactory(typeof(MyType))]
public partial class MyTests
{
    private sealed class MyType
    {
        public required int SomeInt { get; set; }
        public string? SomeString { get; init; }
    }
}

Generated code emits o.SomeInt = ...; and o.SomeString = ...; as separate statements after new MyType(), which fails to compile.

Fix

I have a fix and will open a PR shortly: split properties into an init-only/required bucket and a regular mutable bucket. The former get resolved into temp variables before construction and assigned inside the object-initializer block of the new expression; the latter keep the existing conditional post-construction assignment. Verified against init-only classes, required classes, records with additional init properties, structs with required members, nested required reference-typed properties, and a self-referencing required property forced through the recursion guard.