mlx/CMakeLists.txt: search includes in project dir first

Without this, mlx fails to build in the presence of previous versions of
its headers in the system include directory.

--- mlx/CMakeLists.txt.orig	2026-05-12 15:26:52
+++ mlx/CMakeLists.txt	2026-05-12 15:27:07
@@ -24,6 +24,7 @@
 add_library(mlx_version OBJECT ${CMAKE_CURRENT_SOURCE_DIR}/version.cpp)
 target_compile_definitions(mlx_version PRIVATE MLX_VERSION="${MLX_VERSION}")
 target_include_directories(mlx_version PRIVATE ${PROJECT_SOURCE_DIR})
+target_include_directories(mlx BEFORE PRIVATE ${PROJECT_SOURCE_DIR})
 target_link_libraries(mlx PRIVATE $<BUILD_INTERFACE:mlx_version>)
 
 # Do not export symbols by default.