fix(qemu): set qemu_proj_path for QemuApp correctly

[hfudev]

closes #366

[Copilot]

Pull Request Overview

This PR fixes the qemu_prog_path property in the QemuApp class by converting it from a property to an instance attribute that can be set during initialization. This allows users to specify a custom QEMU program path when creating a QemuApp instance.

• Converts qemu_prog_path from a computed property to a configurable instance attribute
• Adds a new optional parameter qemu_prog_path to the __init__ method
• Sets the attribute during initialization with fallback to the default format

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