Resolves build issues with the extension example (#419)

* resolved extension build issues and added test to ci

* missing gguflib

* rebased

* force mlx install from fix branch

* linux build issue

* point to git install and comment out ci tests

mlx/io/CMakeLists.txt

@@ -14,6 +14,11 @@ target_include_directories(
     $<BUILD_INTERFACE:${json_SOURCE_DIR}/single_include/nlohmann>
     $<INSTALL_INTERFACE:include/json>
 )
+install(
+    DIRECTORY ${json_SOURCE_DIR}/
+    DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/json
+    COMPONENT json_source
+)
 
 MESSAGE(STATUS "Downloading gguflib")
 FetchContent_Declare(gguflib
@@ -26,6 +31,12 @@ target_include_directories(
     $<BUILD_INTERFACE:${gguflib_SOURCE_DIR}>
     $<INSTALL_INTERFACE:include/gguflib>
 )
+install(
+  DIRECTORY ${gguflib_SOURCE_DIR}/
+  DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/gguflib
+  COMPONENT gguflib_source
+)
+
 add_library(
   gguflib STATIC
   ${gguflib_SOURCE_DIR}/fp16.c