Add a class UnpersistedEventContext to allow for the batching up of storing state groups (#14675)
* add class UnpersistedEventContext
* modify create new client event to create unpersistedeventcontexts
* persist event contexts after creation
* fix tests to persist unpersisted event contexts
* cleanup
* misc lints + cleanup
* changelog + fix comments
* lints
* fix batch insertion?
* reduce redundant calculation
* add unpersisted event classes
* rework compute_event_context, split into function that returns unpersisted event context and then persists it
* use calculate_context_info to create unpersisted event contexts
* update typing
* $%#^&*
* black
* fix comments and consolidate classes, use attr.s for class
* requested changes
* lint
* requested changes
* requested changes
* refactor to be stupidly explicit
* clearer renaming and flow
* make partial state non-optional
* update docstrings
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Co-authored-by: Erik Johnston <erik@matrix.org>
03bccd542b