Development: Make 'ready in' 195ms faster (#83628)
## What?
The Watchpack instance created defaulted to `aggregateTimeout: 200`
which causes 200ms of dead time during bootup, affecting the `ready in`
logline.
Before:
```
✓ Starting...
✓ Ready in 583ms
```
After:
```
✓ Starting...
✓ Ready in 355ms // -39.1%
```
Next up:
- `~50ms`: Remove loading webpack when Turbopack is used (it still gets
required currently for `next.config.js`)
- `~110ms`: Figure out how to avoid loading TypeScript which is used to
check `tsconfig.json` options.
