macos-15-xcode-16 image build

Related to macOS Sequoia 15 and Xcode 16 job image (gitlab-org/ci-cd/shared-runners/infrastructure#250 - moved)

Adds macos-15 base build, updated toolchain and Xcode 16 build.

Other related changes:

• Update tart packer plugin for all image builds in the hope for better stability.
• Use tart ip --wait in tests to reduce some fragility.
• Adjust some ansible and rspec to deal with lack of spctl functionality in 15.
• Use ansible_python_interpreter=auto_silent to hide interpreter discovery warnings in logs.