CreatedAt metadata property mapping issue

[sbalocky]

Hi team,

After upgrading from Marten v8.* to v9.2, the CreatedAt metadata property is no longer mapping correctly to my entity model. Other metadata properties (LastModified and Revision) are still mapping without any issues.

Steps to Reproduce / Configuration:

options.Schema.For<WebToSmsProgress>()
       .DatabaseSchemaName(schema)
       .Metadata(m =>
        {
            m.LastModified.MapTo(f => f.LastModifiedOn);
            m.CreatedAt.MapTo(f => f.CreatedOn); // <--- Failing to map in v9
            m.Revision.MapTo(f => f.Version);
        });

The entity gets created via a projection:

    public static async Task<WebToSmsProgress> Create(IQuerySession session, RequestedEvent @event)
    {
        SendSmsInboundData? data = await session.Query<SendSmsInboundData>().SingleOrDefaultAsync(f => f.Id == @event.SmsDataReferenceId);

        if (data is null)
        {
            return null!;
        }

        WebToSmsProgress progress = WebToSmsProgress.CreateInstance(
            @event.TransactionId,
            @event.ConfigurationId,
            @event.SmsDataReferenceId,
            @event.StreamId,
            MessageValidity.CreateInstance(@event.ValidUntil),
            requestReceivedOn: @event.RequestReceivedOn,
            progressData: new(Configuration: data.CurrentConfig, RecipientPhoneNumbers: data.RecipientPhoneNumbers));

        return progress;
    }

Actual Behavior:
When loading the data from the database, the createdOn property remains at its default DateTime value (0001-01-01), while lastModifiedOn and version populate correctly:

{
   "id": "f7492149-22f9-4ff3-9909-7cc6d206abf7",
   "version": 3,
   "streamId": "f7492149-22f9-4ff3-9909-7cc6d206abf7",
   "createdOn": "0001-01-01T00:00:00+00:00",
   "isArchived": false,
   "validUntil": "2026-05-29T00:53:55.1291389+02:00",
   "abortReason": "None",
   "lastModifiedOn": "2026-05-28T10:53:55.966507+00:00"
}

Expected Behavior:
The CreatedAt metadata should populate the CreatedOn property on the model just as it did in Marten v8.