Einops now can use array API to manipulate tensors

Hi folks, a small announcement:

Einops just gained support for API-compliant tensors:

```python
from einops.array_api import rearrange, reduce, repeat, pack, unpack
from numpy.array_api import zeros

x = zeros([2, 3, 4, 5])
rearrange(x, 'b h w c -> b c h w').shape
```

This is already available for testing:

```sh
pip install einops==0.7.0rc1
``` 
