fix: handle `set_isolation_level` gracefully

[caiohamamura]

Whenever the sqlachemy tries to use set_isolation_level without it being defined it will cast object has no attribute 'set_isolation_level' instead of gracefully handling the error by explicitly raising NotImplementedError

[Mause]

hey there, thanks for submitting this PR! any chance we could see a test demonstrating the issue and proving that it's fixed?

[caiohamamura]

You can check this by using:

from sqlalchemy import create_engine

eng = create_engine("duckdb:///:memory:", execution_options={"isolation_level": "AUTOCOMMIT"})
try:
    conn = eng.connect()
except NotImplementedError:
    print('Expected not implemented error raised!')
except Exception as e:
    raise(e)

This will allow other libraries using duckdb-engine to more gracefully handle expected errors, since engine PGDialect implements set_isolation_level, but duckdb does not.

[caiohamamura]

I rebased against main for merging!

[caiohamamura]

Or if you want to wrap it within unittest for automated tests:

from sqlalchemy import create_engine
import unittest

class TestDuckDBDialect(unittest.TestCase):
    def test_set_isolation_level_not_supported(self):
        eng = create_engine("duckdb:///:memory:", execution_options={"isolation_level": "AUTOCOMMIT"})
        with self.assertRaises(NotImplementedError): 
            eng.connect()
            eng.dispose()

if __name__ == '__main__':
    unittest.main()