Add health check method

[razor-x]

Add property that is updated via background polling

const seam = new Seam()
seam.isHealthy // boolean

Allow configuring behavior

const seam = new Seam({
  pollHealth: true
})
seam.isHealthy // false
// first health check happens right away, but needs to wait for at least next tick to update
await sleep(500)
seam.isHealthy // true

```ts
const seam = new Seam({
  pollHealth: {
    pollingInterval: 1000,
    timeout: 5000, // timeout error will set isHealthy false
    onError: (err: Error) => { console.log(err) }
  },
})
seam.isHealthy // false
await sleep(500)
seam.isHealthy // true

const seam = new Seam({
  pollHealth: false
})
seam.isHealthy // false
await seam.updateHealth()
seam.isHealthy // true

By default, { pollHealth: false }.
The seam.isHealthy property should be implemented as a getter and will start false. It should throw if accessed but { pollingInterval: false } or seam.updateHealth was not called at least once.