OpenMetrics support for textfile collector

Currently prometheus_client.exposition.write_to_textfile doesn't support the OpenMetrics text format, which I'm addressing with this (private) hack:

from prometheus_client.openmetrics.exposition import (
    generate_latest as generate_latest_openmetrics,
)
from prometheus_client.registry import CollectorRegistry

def write_openmetrics_to_textfile(path: str, registry: CollectorRegistry) -> None:
    """
    Fork of `prometheus_client.exposition.write_to_textfile`, as the project
    didn't provide an OpenMetrics variant of this helper function.
    """
    with open(path, "wb") as fp:
        fp.write(generate_latest_openmetrics(registry))

Would your project be interested in a non-hacky (as is the case above) OpenMetrics support for textfile collector?

prometheus_client.exposition.write_to_textfile から始め、その動作を prometheus_client.openmetrics.exposition.generate_latest と比較します。既存のテキストファイル collector の動作を維持しながら、helper が OpenMetrics 出力をどのように公開すべきかを判断します。提供された registry に対してサポート対象の helper が有効な OpenMetrics テキストを書き込み、プロジェクトの関連テストでカバーされていれば完了です。