Add History stream

[jonmmease]

Overview

This PR adds a History stream type. History stream instances wrap another stream and collect a history of the values taken on by that stream. This list of states is as the values property

Motivation

A follow-on PR will refactor link_selections to be based on Derived (#4532) and History streams, making it possible for uncollate (See #4551) to extract the linked streams from result of link_selections.

But, this is a simple and generally useful stream type, so I wanted to split it out into its own PR.

Example Usage

Val = Stream.define("Val", v=0.0)
history = History(val)
prihnt(history.contents)

{"values": [{"v": 1.0}]}

# Perform a few updates on val stream
val.event(v=2.0)
val.event(v=3.0)
print(history.contents)

{"values": [{"v": 1.0}, {"v": 2.0}, {"v": 3.0}]}

history.clear_history()
print(history.contents)

{"values": []}

[jlstevens]

Seems like an uncontroversial addition to me! Happy to merge when you think it is ready.

[jonmmease]

It's ready on my end. Thanks @jlstevens

[github-actions]

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