feat: add new variant of the state object with a history

[hollandjg]

Add a new variant of the state object with a history.

ToDos

Implementation

• Make a new object which handles the history by storing the initial object and all the Delta updates added to it.
• Make helper functions – both as stand-alones and methods on the history – which:
  • Filter a history until the last time a particular tag was found, e.g. meta="raw" or meta="clean"
  • Filter just the entries in a history which updated a particular field
  • Show all the version of a particular field in the history
  • Reconstruct a new object from a history
• Make delta_to_state_transformed – a new version of the wrapper delta_to_state which allows transforming the input State before passing it to the inner function, but adds the Delta to the original input State.
  • Write doctests which make sense. What's the simplest possible use for that kind of object?
  • Decide whether this should be a separate function or be merged into the original delta_to_state.
• Add history methods for aggregating things like "experiment_data" over the whole of a history, overriding the "replace" and just putting them all together. This needs to return a State too.
• Make a wrapper @tag_delta which adds a tag like meta="filtered" or component="theorist" to a Delta before passing it back to the caller.

Documentation

• Add an example of using the new state for a cycle involving replacing experiment data with filtered experiment data.

Cleanups

• Decide whether to keep the History version of the StandardState – it's a bit of a mess, as it keeps the history in two places. Probably delete this?

[hollandjg]

I'm not sure we should keep this file and this object – it's a bit weird.

[hollandjg]

This is going to be the standard state we'd use with the history – it's the one which makes the most sense, I think. Although what do we do if a function needs multiple models? There's only one slot for a model here, so I'm not sure how we deal with that.

[hollandjg]

This file is the main change. It adds the History and the State object which uses it: DeltaHistory. There's a few examples and some testing in here.

[hollandjg]

These are changes to the basic state adding so that we don't have to emit a warning if there's a field missing in the Delta, which may often be the case for metadata fields.

[hollandjg]

Starting notebook on examples.