Fix: Bind browser close output to creation context

[mh105]

Reference issue (if any)

None

What does this implement/fix?

In Jupyter notebook, closing a second or more Raw.plot() Qt browser appends its Channels marked as bad: report to the output of the first browser cell rather than the cell that created that browser. This behavior is a bit counterintuitive, since I expect to see the "Channels marked as bad:" message to appear in the same cell I invoke the function.

I asked Codex to look into the issue, and it found that IPykernel associates output with a ContextVar. A persistent Qt event-loop task will retain the context of the cell that initialized it, so a later close callback runs with an older output parent even though MNE’s logger writes to the current sys.stdout.

Codex proposed a minimal change by capturing contextvars.copy_context() independently when each MNE browser is created, then runs the existing shared close implementation in that captured context. The change looks good to me.

Additional information

Codex-generated tests passed:

• Focused browser-context unit tests passed (3 passed).
• Matplotlib browser selection-child close smoke test passed.
• A real IPykernel 7.3.0 plus Qt two-browser probe reproduced the stale parent before the fix and routed each close report to its own cell after the fix.

[larsoner]

I think we'll need a bit more info in the code for the next person to follow. Can you link to some ipython / jupyter docs that talk about this as a potential solution? A quick search turned up ipython/ipython#11565 but maybe there is something better.

Also, is this something we should special-case to the matplotlib inline backend? (Or maybe we don't need to because it's harmless on any others?)