feat: add live MDA status line

[gcharvin]

Summary

Add a small selectable status label to the MDA widget that reports acquisition progress while a sequence is running.

It includes:

• frame count and expected total
• current position/time/z indices when available
• channel name when available
• step state such as preparing, acquiring, autofocus, waiting, paused, canceled, finished, or error

Background

This came from using the GUI during TiEclipse MDA runs, where it was hard to tell whether the acquisition was waiting for the next event, still acquiring, paused, or finished.

Validation

• python -m ruff check src/pymmcore_gui/actions/widget_actions.py
• python -m compileall -q src/pymmcore_gui/actions/widget_actions.py

[codecov]

Codecov Report

❌ Patch coverage is 98.11321% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.94%. Comparing base (76024ca) to head (02dedc6).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/pymmcore_gui/actions/widget_actions.py	98.11%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #161      +/-   ##
==========================================
+ Coverage   81.84%   82.94%   +1.10%     
==========================================
  Files          29       29              
  Lines        1807     1912     +105     
==========================================
+ Hits         1479     1586     +107     
+ Misses        328      326       -2     

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[tlambert03]

thanks @gcharvin, this feature is definitely critical. (screenshot for others to see what it adds)

It's something we've mocked up in various places in different ways (see pymmcore-plus/pymmcore-widgets#268 and also on our "bleeding edge" feature branch "christina ")

So, we can just merge this as strictly better than what we already have, but it might undergo visual structural changes. Specifically, I think the global status bar might be a better target for this info.

In general with your PRs, if I really like the idea, but had envisioned a different implementation, do you want me to just do it (either as changes to your PR or in a new PR)? or request changes and let you make them?

[tlambert03]

side note: that one test fail here is genuinely due to this branch... The point is that signals from the core are not emitted synchronously on the main thread, so if you want to make assertions about widget state following some change, you should generally either use qtbot.waitUntil, or qtbot.waitSignal to ensure that the trigger has happened before checking the widget state