[Feature] Allow order list start from custom number

[edcaron]

Initial checklist

• I agree to follow the code of conduct
• I searched issues and discussions and couldn’t find anything (or linked relevant results below)

Affected packages and versions

crepe latest

Link to runnable example

No response

Steps to reproduce

1. go to https://milkdown.dev/playground
2. type '4. test'

Expected behavior

when Y type '4. test' it should create a ordered list but starting at 4

Actual behavior

After typing '4. test'. The ordered list is created but it starts at 1 instead of 4 that I typed

Kazam_screencast_00007.mp4

Runtime

No response

OS

No response

Build and bundle tools

No response