runners: add and improve QEMU runner (Python-based replacement for qemu.cmake)

[ritesh006]

This PR introduces a Python-based QEMU runner (scripts/west_commands/runners/qemu.py)
as part of the effort to deprecate the legacy cmake/emu/qemu.cmake.

Key points:

• Implements a ZephyrBinaryRunner subclass for QEMU
• Supports --qemu-binary, --qemu-arg, and serial backends (stdio, fifo, pty)
• Provides RunnerCaps(run=True) for consistent west run integration
• Cleans up temporary FIFOs safely after execution
• Adds a deprecation shim in cmake/emu/qemu.cmake

Tested on:

• qemu_x86 board running samples/hello_world (successful boot and output)
• Zephyr SDK 0.16.x with QEMU 8.2.2

This addresses part of zephyrproject-rtos/zephyr#5501
and sets the foundation for full migration from CMake to Python-based QEMU runner.

[sonarqubecloud]

Quality Gate passed

Issues
3 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud