Einsum (#1269)

* einsum initial

* fix comma break

* sum axis was wrong

* small cleanups

* python binding

* changed bindings to resemble numpy

* remove todo comment

* comment changes

* add count of operands/inputs

* fail fast if operands list is empty

* ignore comma if no output

* einsum path matching numpy

* getting somewhere with path

* remove print

* it passes the first test

* moved einsum tests to seperate file

* seperated einsum path

* moved einsum naive

* remove space from equation

* fast fail if no operands passed

* update tests and remove printf

* small cleanup

* some more cleanups

* removed python helper file

* ack

* utilize std for finding min in vector

* duplicate def

* remove the tuple as it was unreadable

* moved einsum_naive back to ops

* remaining isn't needed

* avoid creating another set

* cleanup

* greedy path, start of naive einsum

* more einsum

* fix some bugs

* some more fixes, tests pass

* benchmark

* some simplify

* fix einsum and test

Co-authored-by: Angelos Katharopoulos <a_katharopoulos@apple.com>

* add a bunch more tests and fix a bunch more bugs

* some docs nits

---------

Co-authored-by: dc-dc-dc <dgcruz983@gmail.com>
Co-authored-by: Angelos Katharopoulos <a_katharopoulos@apple.com>

ACKNOWLEDGMENTS.md

@@ -10,7 +10,7 @@ MLX was developed with contributions from the following individuals:
 - Nripesh Niketan: Added `softsign`, `softmax`, `hardswish`, `logsoftmax` activation functions. Added `dropout3d` ops. Added `LogicalAnd` and `LogicalOR` ops. Added `clip_grad_norm` along with `tree_reduce`.
 - Juarez Bochi: Fixed bug in cross attention.
 - Justin Deschenaux: Sine, Cosine, arange, randint, truncated normal, bernoulli, lion optimizer, Dropout2d, linear and logistic regression python example.
-- Diogo Da Cruz: Added `tri`, `tril`, `triu`, `tensordot`, `inner`, `outer`, `tile`, `StreamContext`, `stream` and safetensor support.
+- Diogo Da Cruz: Added `tri`, `tril`, `triu`, `tensordot`, `inner`, `outer`, `tile`, `StreamContext`, `stream`, safetensors support, `einsum`, and `einsum_path`.
 - Gabrijel Boduljak: Added `mlx.core.linalg`, implemented `norm` method and `InstanceNorm` layer. Implemented pooling layers and ``Upsample``.
 - Hinrik Snær Guðmundsson: Added `atleast_1d`, `atleast_2d`, `atleast_3d` ops.
 - Luca Arnaboldi: Added `Ceil` and `Floor` ops; implemented pickling, copy and deepcopy for mlx arrays.