Export / import functions to / from a file (#1642)

* export and import functions

* refactor + works for few primitives

* nit

* allow primitives with state

* nit

* nit

* simplify serialize / deserialize

* fix for constants

* python bindings

* maybe fix serialize failure case

* add example

* more primitives, training kind of works

* same result for python and c++

* some fixes

* fix export

* template it up

* some simplificatoin

* rebase

* allow kwargs and multiple functions

* exporter

* more primitives for exporting

* deal with endianness

* handle invalid stream

* add docstring

CMakeLists.txt

@@ -27,6 +27,7 @@ option(BUILD_SHARED_LIBS "Build mlx as a shared library" OFF)
 if(NOT MLX_VERSION)
   set(MLX_VERSION 0.21.1)
 endif()
+add_compile_definitions("MLX_VERSION=${MLX_VERSION}")
 
 # --------------------- Processor tests -------------------------