Treat .NET 7 `required` properties as actually required by default

**Code snippet:**
```cs
public class Options
{
[Option]
public required int Port { get; init; }

[Option]
public required string Server { get; init; }
}
```

**Expected behaviour:** Both `Port` and `Server` are required and the parsing fails if at least on of them is not present.

**Actual behaviour:** They are not required, I still have to specify `[Option(Required = true)]` in order for it to work

首先跟踪如何检查 [Option] 属性，以及如何推断其 Required 设置，注意 issue 中显示的 .NET 7 required 属性。为缺少 Port 和 Server 值的情况添加回归测试覆盖，并验证在没有显式 Required 设置时解析会失败，同时保持现有选项行为不变。

由索引模型根据 Issue 内容生成。