add UUIDv7 generation option

[Funkest]

Add optional uuidV7 parameter to New() and NewXXX() methods. When set to true, the methods use Guid.CreateVersion7().
This feature is only available when targeting .NET 9.0 or later by preprocessor directive.

[neuecc]

Thank you, I think it's good.
However, since it's an overload, isn't it better to just use New(bool uuidV7) rather than New(bool uuidV7 = false)?

[kase-sanwa]

I agree completely. I wonder why I didn't write that myself.

[neuecc]

ok, thanks! I'll release soon!