Modernize tooling for LTS Linux and macOS 27

[mjchaker]

This updates the development and test workflow so QIRA works with current LTS Linux and macOS 27 beta environments, where the legacy Python 2 and old distro assumptions no longer hold.

What changed

• Switched install/test scripts to modern Python 3 tooling (python3 -m venv, python -m pip, pytest) with safer shell defaults.
• Refreshed requirements.txt from legacy pins to modern compatible ranges, and kept ipaddr for current middleware behavior.
• Updated Docker from Ubuntu 16.04 to Ubuntu 24.04 and moved image setup to Python 3 venv flow.
• Updated README OS/install guidance to reflect current support expectations (Linux-first with macOS limitations around QEMU tracer).
• Fixed Cython import resolution in middleware/qiradb/qiradb.pyx for current Cython include behavior.
• Made Linux-only tracer/integration behavior explicit in tests so macOS runs skip unsupported QEMU tracer execution instead of hard-failing.

Notes for reviewers

• QEMU user tracer remains Linux-only by design; macOS coverage now focuses on supported components.
• The test script keeps integration coverage on Linux and avoids false negatives on non-Linux hosts.