Save checkpoints in a run-specific dir with config file.

[HoagyC]

This changes pipeline.py so that checkpoints from a run are saved in a folder labelled by the starting time of the run. It also saves a json with the config in the file.

Also adds the git hash to the saved config file so that we can trace which version of the code a model was run with.

[alan-cooney]

We could also use the release version of sparse_autoencoder? Might be a bit more readable (and would also work for anyone who pip installs the lib). This can then be set in the checkpoint metadata

Note this would need to setup https://setuptools-git-versioning.readthedocs.io/en/v1.13.5/index.html

[alan-cooney]

Let me know what you think - happy to sort the merge conflicts myself afterwards btw

[HoagyC]

Hey, been looking into this, seems like I can use importlib.metadata.version? Might be wrong somehow but setuptools integration with Poetry seems fiddly.