format() broken for duration objects (undefined values, wrong format, inconsistent behaviour)

**Describe the bug**
Every duration instance I create whether from ISO-string or from object appears to be broken.
The behaviour is also inconsistent between construction from ISO-string or object.

### Case 1 (init leaves undefined values, inconsistent):
```js
dayjs.duration({ seconds: 20 }).format('HH:mm:ss:SSS');
// received: undefined:undefined:20:undefined
// wanted: 00:00:20:000
```
and weirdly:
```js
dayjs.duration('PT20S').format('HH:mm:ss:SSS');
// received: 00:00:20:undefined
// wanted: 00:00:20:000
```

### Case 2 (milliseconds parsing from ISO string):
```js
dayjs.duration({ hours: 1, minutes: 2, seconds: 3, milliseconds: 4 }).format('HH:mm:ss:SSS');
// received: 01:02:03:004
// wanted: 01:02:03:004
```
but from ISO string, parsing is completely broken:
```js
duration = dayjs.duration('PT1H2M3.004S').format('HH:mm:ss:SSS');
// received: 01:02:3.004:undefined
// wanted: 01:02:03:004
```

### Case 3 (overflows not calculated on creation):
```js
dayjs.duration({ seconds: 180 }).format('mm:ss');
// received: undefined:180
// wanted: 03:00
```

### Case 4 (overflow calculation ignores format options)
```js
dayjs.duration({ hours: 23, minutes: 30 }).add(3, 'h').format('HH:mm');
// received: 02:30
// wanted: 26:30
```

## Workaround
Cases 1,2,3 can be worked around by adding nothing (`.add(0,'s')`), like:
```js
// for case 1
dayjs.duration({ seconds: 20 }).add(0,'s').format('HH:mm:ss:SSS');
// received: 00:00:20:000

// for case 2
dayjs.duration('PT1H2M3.004S').add(0,'s').format('HH:mm:ss:SSS');
// received: 01:02:03:004

// for case 3
dayjs.duration({ seconds: 180 }).add(0,'s').format('mm:ss');
// received: 03:00
```

@iamkun Feels like you forgot to call an init function inside the constructor.

**Information**
- Day.js Version 1.10.7
- OS: macOS
- Browser latest and greatest
- Time zone: Europe/Berlin

Reproduce the four duration examples, including ISO-string and object construction, then trace the duration construction, parsing, format, and add entry points. Done means the shown cases produce the expected zero-padded values, normalize overflows on creation, and preserve hour overflows according to the format.

Written by the indexing model from the issue text.