[rootvector2]

Description

Fix memory leak in GetContext() in jxl_cms.cc where cmsCreateContext allocates a CMS context per thread but cmsDeleteContext is never called on thread exit.

Replaced raw void* with std::unique_ptr using a custom ContextDeleter, following the existing RAII pattern (ProfileDeleter, TransformDeleter, CurveDeleter) in the same file.

Fixes #4166

[eustas]

LGTM, modulo missing space in line 808.

[eustas]

BTW, the other place where cmsContext is created would need similar change (load_jxl.cc)... But there it is wildly wrong - one context is shared between multiple threads... Creating an issue now, could be addressed later.

[rootvector2]

LGTM, modulo missing space in line 808.

done

[eustas]

Thanks!