reorganize code around result formatting

Code is now organized by api version. So formatting has moved to
the api.v1 module. Instead of holding a separate ResultFormatter
object per result format, simply move the functions to the
formater collector and hand in the requested format as a parameter.
Thus reorganized, the api.v1 module can export three simple functions
for result formatting which in turn makes the code that uses
the formatters much simpler.

test/python/api/test_result_formatting_v1.py

@@ -0,0 +1,57 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# This file is part of Nominatim. (https://nominatim.org)
+#
+# Copyright (C) 2023 by the Nominatim developer community.
+# For a full list of authors see the git log.
+"""
+Tests for formatting results for the V1 API.
+"""
+import datetime as dt
+import pytest
+
+import nominatim.api.v1 as api_impl
+from nominatim.api import StatusResult
+from nominatim.version import NOMINATIM_VERSION
+
+STATUS_FORMATS = {'text', 'json'}
+
+# StatusResult
+
+def test_status_format_list():
+    assert set(api_impl.list_formats(StatusResult)) == STATUS_FORMATS
+
+
+@pytest.mark.parametrize('fmt', list(STATUS_FORMATS))
+def test_status_supported(fmt):
+    assert api_impl.supports_format(StatusResult, fmt)
+
+
+def test_status_unsupported():
+    assert not api_impl.supports_format(StatusResult, 'gagaga')
+
+
+def test_status_format_text():
+    assert api_impl.format_result(StatusResult(0, 'message here'), 'text') == 'OK'
+
+
+def test_status_format_text():
+    assert api_impl.format_result(StatusResult(500, 'message here'), 'text') == 'ERROR: message here'
+
+
+def test_status_format_json_minimal():
+    status = StatusResult(700, 'Bad format.')
+
+    result = api_impl.format_result(status, 'json')
+
+    assert result == '{"status": 700, "message": "Bad format.", "software_version": "%s"}' % (NOMINATIM_VERSION, )
+
+
+def test_status_format_json_full():
+    status = StatusResult(0, 'OK')
+    status.data_updated = dt.datetime(2010, 2, 7, 20, 20, 3, 0, tzinfo=dt.timezone.utc)
+    status.database_version = '5.6'
+
+    result = api_impl.format_result(status, 'json')
+
+    assert result == '{"status": 0, "message": "OK", "data_updated": "2010-02-07T20:20:03+00:00", "software_version": "%s", "database_version": "5.6"}' % (NOMINATIM_VERSION, )