Allow range selector to work for sub-second steps

I commonly have time series dataframes with sub-second frequencies (milli/micro/nano) and I would like to use Scatter plots with rangeselector to visualize them. Issue is rangeselector's buttons can only be provided with a step included in the following:

['month', 'year', 'day', 'hour', 'minute', 'second', 'all']

I would like to be able to pass as well: nanosecond, microsecond, and millisecond.

I am not familiar with the plotly.py codebase but I am happy to open a PR provided I can have some guidance.

まず、plotly.py が Scatter プロットの rangeselector ボタンをどのように検証またはシリアライズするかを追跡し、issue で指定されている許可された step 値に注目します。nanosecond、microsecond、millisecond の step で rangeselector を実行し、結果のプロット設定が受け入れられることを確認して、変更を検証します。