Replace AssertionErrors with more meaningful errors

[mariosasko]

Replace the AssertionErrors with more meaningful errors such as ValueError, TypeError, etc.

The files with AssertionErrors that need to be replaced:

src/datasets/arrow_reader.py
src/datasets/builder.py
src/datasets/utils/version.py

[galbwe]

Hi, can I pick up this issue?

[galbwe]

#self-assign

[galbwe]

Looks like the top-level datasource directory was removed when #4974 was merged, so there are 3 source files to fix.