reader: mf4: test for 'S' type .Dir like asammdf

[tuna-f1sh]

I could not decode a mf4 file created by mdflib. It creates .Dir channels with string values not int: https://github.com/ihedvall/mdflib/blob/main/mdflib/src/canconfigadapter.cpp#L321

Not sure if this is standard in MDF but since the note said the reader iterators are based on the asammdf GUI code, I took a look. It does a check on the attached type.

Commit adds the same for python-can so that it can decode files with a string value for .Dir.

[zariiii9003]

According to the standard, it should be 0 or 1.

[tuna-f1sh]

Ah ok - unfortunately I don't have access to the specification. I'll create an issue in mdflib instead then. Are you able to provide a snippet of the spec saying this? Do you know why asammdf would support values as string? Is there some legacy non-explicit definition here?

[zariiii9003]

The spec says it's a bit signal, not a string:

According to the asammdf commit message, it was added to fix CANalyzer measurements.

Anyhow, i guess there's no harm in merging, since this does not affect the files we produce. Could you fix the formatting?

[tuna-f1sh]

Yes I've updated commit with black format.