Migrate GUI framework from PyQt5 to PyQt6

[GiGiKoneti]

Summary

PyQt5 (and its underlying Qt5) officially reached End-of-Life on May 26, 2024. eSim currently pins PyQt5==5.15.7 in requirements.txt, meaning the entire GUI layer runs on an unsupported framework that will no longer receive security patches or bug fixes.

This issue proposes migrating the GUI codebase from PyQt5 → PyQt6 to future-proof the application.

Scope of Changes

Based on an audit of the src/ directory, the migration touches ~42 Python files across the following categories:

Category	Details
Import rewrites	from PyQt5 → from PyQt6 across all modules
Module relocations	QAction moved from QtWidgets → QtGui in Qt6
Deprecated methods	.exec_() → .exec() (~85 call sites)
Scoped enums	PyQt6 enforces fully qualified enums (e.g. Qt.Vertical → Qt.Orientation.Vertical)
Removed APIs	AA_DontUseNativeDialogs attribute removed in Qt6
Dependencies	requirements.txt updated to PyQt6>=6.5.0

Motivation

• Security: No more upstream patches for Qt5/PyQt5 vulnerabilities.
• Compatibility: Newer Linux distros and Python versions are dropping PyQt5 from their package repos.
• Ecosystem: Downstream tools (matplotlib, etc.) are progressively moving to Qt6 backends.

References

• Qt 5 End-of-Life announcement
• PyQt6 migration guide
• Historical precedent: PR ported GUI to PyQt5; platform independent paths; launch ngspice through mintty on Win OS #156 migrated eSim from PyQt4 → PyQt5 in 2020.