Updated get_bufr to separate station position from bufr

* The station position determination (AWS_latest_locations) is separated from the bufr file export
* Updated the unit tests

Corrected minimum data check to allow p_i or t_i to be nan

Renamed process_station parameters for readability
* Rename now_timestamp -> target_timestamp
* Rename time_limit -> linear_regression_time_limit

Applied black

src/pypromice/postprocess/create_bufr_files.py

@@ -59,9 +59,9 @@ def create_bufr_files(
                 input_files=input_files,
                 store_positions=False,
                 positions_filepath=None,
-                time_limit=DEFAULT_LIN_REG_TIME_LIMIT,
+                linear_regression_time_limit=DEFAULT_LIN_REG_TIME_LIMIT,
                 timestamps_pickle_filepath=None,
-                now_timestamp=period,
+                target_timestamp=period,
                 station_configuration_mapping=station_configuration_mapping,
                 positions_seed_path=DEFAULT_POSITION_SEED_PATH,
                 break_on_error=break_on_error,