dayjs().add(dayjs.duration()) inconsistency

**Describe the bug**
https://stackblitz.com/edit/vitejs-vite-rvrdyd?file=main.js

when added a duration which is initialized with weeks, the dayjs.add function does not add any time.

**Expected behavior**
Should give correct output

**Information**
- Day.js Version: 1.11.13
- OS: macOS
- Browser: latest chrome
- Time zone: GMT+05:30

Start by running the linked StackBlitz reproduction in main.js and confirm how a duration initialized with weeks behaves when passed to dayjs().add(). Trace the duration and add handling, then verify that week-based durations produce the expected added time.

Written by the indexing model from the issue text.