Fix macos-latest build

[NealsSec]

Problem

I noticed some QT modules were not being linked in macos-latest stable which was causing a crash on start on MacOS 26 and 27. I believe the root of the problem was echo "/usr/local/opt/qt@6/bin" >> $GITHUB_PATH points to the intel homebrew path instead of the arm path.

Solutions

• My remedy is to use https://github.com/jurplel/install-qt-action locked to qt 6.11.*, This adds everything qt6 related to the path automatically.
• I explicitly install libusb and pkgconf via brew for determinism and I update the PKG_CONFIG_PATH accordingly.
• I've transitioned from pcre -> pcre2 as pcre is deprecated. I may look at replacing this with some sed in the future though.

I think this same fix can be applied to the LibreVNA gui, I'll probably work on that after we merge this here.

This may close #34

I do not have a librevna/librecal of my own so I'm working on borrowing a set for testing, if you could test this on your end as well it would help a lot.

[NealsSec]

• Decided to drop installing the pkgconf and libusb from brew and just default to using the version bundled with the runner's xcode.
• Dropped pcre2 and used sed for the version numbers instead

Managed to borrow my buddy's set today for testing today. LibreCAL-GUI starts properly on MacOS 27.0.1 and connects to the instrument.

There will be a similar PR in the LibreVNA repo that largely mirrors this one.

[jankae]

Thank you so much for taking a look at this. I can not test this on my side due to lack of macos hardware (otherwise I would have fixed this myself a long time ago).

I'll take your word for it and merge it as is.