-type hackney_global_measurements() :: finished_requests | nb_requests | total_requests.
-type hackney_host_measurements() ::
    connect_error
    | connect_time
    | connect_timeout
    | nb_requests
    | request_time
    | response_time.
-type hackney_pool_measurements() ::
    free_count | in_use_count | no_socket | queue_count | take_rate.
-type hackney_global_metric() :: list().
-type hackney_host_metric() :: list().
-type hackney_pool_metric() :: list().
-type hackney_generic_metrics() :: nb_requests | total_requests | finished_requests.
-type hackney_host_metrics() ::
    nb_requests
    | request_time
    | connect_time
    | response_time
    | connect_timeout
    | connect_error
    | new_connection
    | reuse_connection.
-type hackney_pool_metrics() ::
    take_rate | no_socket | in_use_count | free_count | queue_count.
% -type hackney_metric() :: [hackney, hackney_generic_metrics()] | [hackney, any(), hackney_host_metrics()] | [hackney_pool, atom(), hackney_pool_metrics()].
-type hackney_metric() :: list().
-type metric_type() :: counter | gauge | histogram | meter.
-type transform_fun() :: fun((any(), any()) -> any()).
-type keyword() :: {atom(), any()}.
-type keywords() :: [keyword()].