don't work with new c# version namespace format

Hello!
Great library, but it doesn't generate builder with files using C# 10 namespace formats.
Works good:
```
namespace SomeName
{
    [GenerateDataBuilder]
    class A
    {
    }
}
```

Don't work:
```
namespace SomeName;

[GenerateDataBuilder]
class A
{
}
```
Described the problem in case someone repeats it.
Thank for attention!

