Add closeActiveConnections to server.stop(), like exists in native bun

[Flaque]

This fixes #806, by adding support for Bun server's native closeActiveConnections?: boolean option on server.stop().

const app = new Elysia()
     .get("/", () => 'hi')
     .listen(3000)

// The boolean argument here is optional, new, and mimics native bun.
app.stop(true) // Abruptly any requests inflight