ASCReader does not support ASC format since V8.1

### Describe the bug

ASCReader in python-can 4.1.0 doesn't support ASC CANFD format since V8.1, since \ name is missing in code.
According to the document from Vector , there should be \ between \ and \.

### To Reproduce

Use python-can to read CANFD message in asc log since format V8.1.

### Expected behavior

Reading process stopped with CANFD message.

### Additional context
I made a quick fix in a forked [branch](https://github.com/Tian-Jionglu/python-can/tree/asc_quick_fix).
I think an overall fix about ASC format IO is needed in this issue.

OS and version:
Python version:
python-can version:
python-can interface/s (if applicable):

Traceback and logs