ipympl changes MPL backend on import

• xref: https://github.com/mne-tools/mne-python/pull/13963#pullrequestreview-4499976618

In mne-python (see above), we have a functionality called sys_info, which gives us (among other things) the versions of all sorts of installed packages.

For this reason, we also import ipympl.

At import time, ipympl actually changes the MPL backend.

Is this something that could be avoided? This change in backend was very surprising to us and it took an in-depth profiling to identify it as the cause of a massive memory leak in a pipeline that produced several plots on each iteration, never closing them due to the backend change.

issueおよびリンク先のmne-python pull requestのレビューで説明されているimport時の挙動を確認し、ipymplのimportによってMatplotlibのbackendが変更される箇所に焦点を当ててください。sys_info形式のimportシーケンスでこれを再現し、ipymplをimportしてもbackendが変更されず、報告されているplotのライフサイクル問題も発生しないことを検証してください。