[ESI] Add readable `__version__` attribute to esiaccel package

Currently, neither `__init__.py` nor any of the setup/wheel build stuff for the esiaccel python package defines a `__version__` attribute. This would be handy for users to be able to runtime verify that a required esiaccel package is available, i.e. through
```py
import esiaccel
print(esiaccel.__version__)
```

There seems to be a variety of ways/options to inject this, based on how the wheel is built - [some inspiration](https://github.com/llvm/circt/blob/930aabe70fe78965a153f6e936c5853e948873eb/lib/Dialect/ESI/runtime/python/esiaccel/__init__.py).