[pixi-build-ros] Windows: cmake_install.cmake fails with "Invalid character escape" for any ament_cmake package with rosidl-generated Python bindings #6955

pixi version: 0.78.0
Platform: win-64 (Windows 11), MSVC 2022 (14.44.35207) via the vs2022 compiler variant
Backend: pixi-build-ros (formerly prefix-dev/pixi-build-backends, now part of this repo)

Summary

Building any ROS2 package that generates rosidl Python message bindings (i.e. any
ament_cmake package with .msg/.srv files) fails on Windows during the install
step with a CMake parse error in the generated cmake_install.cmake:

CMake Error at cmake_install.cmake:152 (execute_process):
  Syntax error in cmake code at
    .../build/cmake_install.cmake:154
  when parsing string
    C:\<...>\host\python.exe
  Invalid character escape '\w'.

Root cause (as far as I can tell)

The generated cmake_install.cmake contains this block:

execute_process(
      COMMAND
      "C:\wsbuild\.pixi\bld\ros-jazzy-wasp-as-interfaces\8WF_D-nh4o0\host\python.exe" "-m" "compileall"
      "C:/wsbuild/.pixi/bld/ros-jazzy-wasp-as-interfaces/8WF_D-nh4o0/host/Library/../Lib/site-packages/wasp_as_interfaces"
    )

Note the inconsistency: the compileall target path uses forward slashes
(C:/wsbuild/..., valid CMake string cont