make NominatimAPI[Async] a context manager

If close() isn't properly called, it can lead to odd error messages
about uncaught exceptions.

test/python/api/test_api_connection.py

@@ -9,45 +9,34 @@ Tests for enhanced connection class for API functions.
 """
 from pathlib import Path
 import pytest
-import pytest_asyncio
 
 import sqlalchemy as sa
 
-from nominatim_api import NominatimAPIAsync
-
-@pytest_asyncio.fixture
-async def apiobj(temp_db):
-    """ Create an asynchronous SQLAlchemy engine for the test DB.
-    """
-    api = NominatimAPIAsync(Path('/invalid'), {})
-    yield api
-    await api.close()
-
 
 @pytest.mark.asyncio
-async def test_run_scalar(apiobj, table_factory):
+async def test_run_scalar(api, table_factory):
     table_factory('foo', definition='that TEXT', content=(('a', ),))
 
-    async with apiobj.begin() as conn:
+    async with api.begin() as conn:
         assert await conn.scalar(sa.text('SELECT * FROM foo')) == 'a'
 
 
 @pytest.mark.asyncio
-async def test_run_execute(apiobj, table_factory):
+async def test_run_execute(api, table_factory):
     table_factory('foo', definition='that TEXT', content=(('a', ),))
 
-    async with apiobj.begin() as conn:
+    async with api.begin() as conn:
         result = await conn.execute(sa.text('SELECT * FROM foo'))
         assert result.fetchone()[0] == 'a'
 
 
 @pytest.mark.asyncio
-async def test_get_property_existing_cached(apiobj, table_factory):
+async def test_get_property_existing_cached(api, table_factory):
     table_factory('nominatim_properties',
                   definition='property TEXT, value TEXT',
                   content=(('dbv', '96723'), ))
 
-    async with apiobj.begin() as conn:
+    async with api.begin() as conn:
         assert await conn.get_property('dbv') == '96723'
 
         await conn.execute(sa.text('TRUNCATE nominatim_properties'))
@@ -56,12 +45,12 @@ async def test_get_property_existing_cached(apiobj, table_factory):
 
 
 @pytest.mark.asyncio
-async def test_get_property_existing_uncached(apiobj, table_factory):
+async def test_get_property_existing_uncached(api, table_factory):
     table_factory('nominatim_properties',
                   definition='property TEXT, value TEXT',
                   content=(('dbv', '96723'), ))
 
-    async with apiobj.begin() as conn:
+    async with api.begin() as conn:
         assert await conn.get_property('dbv') == '96723'
 
         await conn.execute(sa.text("UPDATE nominatim_properties SET value = '1'"))
@@ -71,23 +60,23 @@ async def test_get_property_existing_uncached(apiobj, table_factory):
 
 @pytest.mark.asyncio
 @pytest.mark.parametrize('param', ['foo', 'DB:server_version'])
-async def test_get_property_missing(apiobj, table_factory, param):
+async def test_get_property_missing(api, table_factory, param):
     table_factory('nominatim_properties',
                   definition='property TEXT, value TEXT')
 
-    async with apiobj.begin() as conn:
+    async with api.begin() as conn:
         with pytest.raises(ValueError):
             await conn.get_property(param)
 
 
 @pytest.mark.asyncio
-async def test_get_db_property_existing(apiobj):
-    async with apiobj.begin() as conn:
+async def test_get_db_property_existing(api):
+    async with api.begin() as conn:
         assert await conn.get_db_property('server_version') > 0
 
 
 @pytest.mark.asyncio
-async def test_get_db_property_existing(apiobj):
-    async with apiobj.begin() as conn:
+async def test_get_db_property_existing(api):
+    async with api.begin() as conn:
         with pytest.raises(ValueError):
             await conn.get_db_property('dfkgjd.rijg')