Yet another macOS save button fix with dialog popup

[amilcarlucas]

Much simpler than #1304

Closes #1264

@OmkarSarkar204 can you please test this one?

[Copilot]

Pull request overview

Updates Tkinter window centering behavior to avoid macOS-specific UI issues when forcing a window refresh.

Changes:

• Add OS detection via platform.system().
• Use update_idletasks() on macOS (Darwin) instead of update() after setting geometry.

[Copilot]

This introduces platform-specific behavior without documenting why macOS needs update_idletasks() while other platforms use update(). Please add a short inline comment explaining the underlying issue/bug being worked around (e.g., what update() triggers on macOS) so future changes don’t accidentally regress it.

[github-actions]

☂️ Python Coverage

current status: ✅

Overall Coverage

Lines	Covered	Coverage	Threshold	Status
11504	10474	91%	89%	🟢

New Files

No new covered files...

Modified Files

File	Coverage	Status
ardupilot_methodic_configurator/frontend_tkinter_base_window.py	95%	🟢
TOTAL	95%	🟢

updated for commit: 5071f6c by action🐍

[github-actions]

Test Results

    2 files  ±0      2 suites  ±0   28m 47s ⏱️ -33s
3 014 tests ±0  3 009 ✅ +2   5 💤 ±0  0 ❌  - 2 
6 028 runs  ±0  6 018 ✅ +2  10 💤 ±0  0 ❌  - 2 

Results for commit 5071f6c. ± Comparison against base commit a686455.

[OmkarSarkar204]

Yes, I tested it and it worked perfectly this time! The popups show up right along with the button without any freezing.

It's amazing how hard I was trying to fix it and how simple your solution was. Thank you for stepping in and doing this. I'm going to review your changes to see where I went wrong.

[amilcarlucas]

Thanks for testing! I merged it to master and will close the other PR