Add method `spinner.message(_msg: string)`

Add method `spinner.message(_msg: string)` that can update message of spinner in progress.

use case:
```typescript
import * as p from "@clack/prompts";

p.intro("spinner start...");

const spin = p.spinner();
const total = 10000;
let progress = 0;
spin.start();

await new Promise((resolve) => {
const timer = setInterval(() => {
progress = Math.min(total, progress + 100);
if (progress >= total) {
clearInterval(timer);
resolve(true);
}
spin.message(`Loading packages [${progress}/${total}]`); // <===
}, 100);
});

spin.stop(`Done`);

p.outro("spinner stop...");
```