regz: depends on microzig when generating standalone

[Leandros]

The generated VectorTable struct depends on microzig.interrupt.Handler and microzig.interrupt.unhandled.

pub const VectorTable = extern struct {
    const Handler = microzig.interrupt.Handler;
    const unhandled = microzig.interrupt.unhandled;
    // ...
};

[tact1m4n3]

You can add an import to the generated file called microzig that provides those definitions. Though, I agree that the standalone option should generate code that does not depend on any imports.