Fix column descriptor wire encoding

[zehiko]

Describe the bug

It seems that after switching to arrow-rs conversion of data type to/from string is broken for the List type. This breaks the schema fetching support and the relevant integration test on the SN side.

We need to figure out a path forward for datatype conversion, fix this and re-enable the integration test on the ReDap side.

Opening here, even though the type conversion happens on the rerun side.
Expected behavior

Conversion of a schema i.e. a list of ColumnDescriptors to and from the wire format (protobuf) should work as expected.