Add unsynced status to AssetSlice

[schrockn]

Summary & Motivation

Adding the ability to interrogate the AssetSlice for its sync status.

We are going to move to the term "unsynced" instead of "stale" or "outdated" to describe the state where a particular partitions underlying representation in storage is not in sync with its software definition. This can be:

• Because the underlying stored partition is missing
• The code version of the asset has changed since the last time this partition was materialized.
• An upstream partition has a new materialization that was not used to materialize the current partition.
• Dependencies have changed
• A direct upstream asset partition is unsynced. (The definition is recursive within some scope)

Internal discussion around this.

How I Tested These Changes

Unit tests

[schrockn]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• Add unsynced status to AssetSlice #20358 👈
• Support dynamic partitioning in AssetSlice #20355 : 1 other dependent PR (#20364 )
• Support multi-partitioning in AssetSlice #20353
• Add AssetGraphView.create_latest_time_window_slice #20352
• AssetGraphView, TemporalContext, and AssetSlice #20312 : 1 other dependent PR (#20385 )
• master

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[schrockn]

Abandoning this as we are going to redefine unsynced