[codex] Fix Windows clang CI build

[L-Sun]

Summary

• Disable ccache/sccache for the Windows clang-cl GitHub Actions job, including the dependency-install phase.
• Keep the Windows workflow on clang-cl only while MSVC remains disabled.
• Fix the playground WinPIX loader to use wide-character Windows APIs when UNICODE is defined.

Root cause

The latest windows-build run first failed before project compilation while xmake installed assimp v6.0.4. On windows-latest, ccache.exe from Strawberry Perl wrapped CMake's cmcldeps resource-compiler invocation and caused the RC /fo argument to be interpreted by clang-cl, ending with clang-cl: error: no such file or directory: '/fo'.

After disabling compiler cache launchers, PR CI progressed into the project build and exposed a real clang-cl compile error in examples/playground/main.cpp: with UNICODE enabled, GetModuleHandle and LoadLibrary resolve to the W variants but were passed narrow strings.

Validation

• xmake f -y -a x64 -m release --toolchain=clang-cl --ccache=n --policies=package.build.ccache:n,build.ccache:n
• xmake build playground
• xmake build

This PR is draft so PR CI can validate the GitHub runner path before merging.