Export DataError from the DB API module

[Mirochill]

Fixes #307.

from tarantool.dbapi import DataError currently fails, preventing PEP 249 clients from catching data errors through the driver module. Export the existing tarantool.error.DataError class alongside the other DB API exceptions.

Add a server-independent regression that checks class identity, the DatabaseError hierarchy, and catching an error raised through tarantool.error. Register it in the normal suite.

Validation on Python 3.13.16:

• The new regression fails with AttributeError on unchanged upstream and passes with this change.
• Full repository Pylint (10.00/10), Flake8, codespell, and git diff --check pass using the pinned test-tool versions.
• Database integration tests were not run; no Tarantool server is installed.

AI assistance was used for the implementation and tests. All reported checks ran locally.