Refactor Metal OCIO shader setup & rendering

Introduce helper utilities and refactor duplicated Metal OCIO logic: add create_default_compile_options and create_ocio_compile_options; add begin_offscreen_render_pass and end_offscreen_render_pass to centralize command buffer/encoder lifecycle; introduce MetalOcioShaderSourceParts and helper builders (append_ocio_* / build_ocio_shader_call_params / append_texture_binding_source) to construct OCIO shader sources and call parameters; factor texture upload loops into upload_ocio_textures_for_dimension and upload_ocio_non_3d_textures; add bind_ocio_fragment_resources to bind fragment uniforms/textures. Update preview pipeline and OCIO preview program to use these helpers, reducing duplication and improving clarity and error handling.

Signed-off-by: Vlad (Kuzmin) Erium <libalias@gmail.com>

Author: ssh4net