Support sqlite as OMOP backend

[eroell]

Description of feature

Suggested approach:

1. Allow sqlite connection to be passed
   

   ehrdata/src/ehrdata/io/omop/_check_arguments.py

   Lines 28 to 30 in 80acdfd

   	def _check_valid_backend_handle(backend_handle) -> None:
   	if not isinstance(backend_handle, duckdb.duckdb.DuckDBPyConnection):
   	raise TypeError("Expected backend_handle to be of type DuckDBPyConnection.")

2. Include sqlite as additional parametrization in test suites
   test_omop.py

3. Fix the tests that break

4. Cover some miscellaneous issues that pop up along this path