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

examples/export/README.md

@@ -0,0 +1,49 @@
+## Setup
+
+Install MLX:
+
+```bash
+pip install mlx>=0.22
+```
+
+Build the C++ examples:
+
+```bash
+cmake -B build -DCMAKE_BUILD_TYPE=Release
+cmake --build build
+```
+
+## Run
+
+### Eval MLP
+
+Run the Python script to export the eval function:
+
+```bash
+python eval_mlp.py
+```
+
+Then run the C++ program to import and run the function:
+
+```
+./build/eval_mlp
+```
+
+The Python and C++ programs should output the same result.
+
+### Train MLP
+
+Run the Python script to export the model initialization and training
+functions:
+
+```bash
+python train_mlp.py
+```
+
+Then run the C++ program to import and run the functions:
+
+```
+./build/train_mlp
+```
+
+The Python and C++ programs should output the same results.