fix(build_ros): normalize Windows CMake paths to forward slashes

[aoright]

Description

When building ROS packages on Windows (such as ament_cmake packages generating rosidl Python message bindings), CMake generates install scripts (e.g. cmake_install.cmake). Because native Windows paths contain backslashes (\), CMake string parsing encounters syntax errors such as Invalid character escape '\w' when executing compileall on PYTHON_EXECUTABLE or LIBRARY_PREFIX.

This PR:

1. Normalizes %PYTHON%, %LIBRARY_PREFIX%, and %SRC_DIR% with forward slashes before passing them to CMake in bld_ament_cmake.bat and bld_catkin.bat.
2. Quotes CMake path definitions to handle paths with spaces or special characters cleanly.
3. Adds unit tests verifying that render_build_script_with_platform renders forward-slash conversions and quoted variables for Windows ament_cmake and catkin builds.

Fixes #6955

How Has This Been Tested?

• Added test_render_ament_cmake_windows and test_render_catkin_windows in crates/pixi_build_ros/src/build_script.rs verifying proper normalization and argument quotation on Windows.
• Ran cargo test -p pixi-build-ros (all 89 tests passed).

AI Disclosure

• This PR contains AI-generated content.
  • I have tested any AI-generated content in my PR.
  • I take responsibility for any AI-generated content in my PR.
    Tools: Claude

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added sufficient tests to cover my changes.