Replace AssertionErrors with more meaningful errors
Hi, can I pick up this issue? #self-assign Looks like the top-level `datasource` directory was removed when https://github.com/huggingface/datasets/pull/4974 was merged, so there are 3 source files to fix.
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
```