ENH: add get_snapshot

[klauer]

Add get_snapshot tool to get PV data (one or more PVs or globs) at a given point in time.

• Added pre-commit config
• Started get_snapshot utility for getting values of multiple PVs at a specific point in time (referred to as save/restore API in the docs)
• Cleaned up some flake8 issues (sorry for the mess)
• To investigate: skipped search() to pattern match via globs if no glob characters were included. Ensure this doesn't mess up any current functionality.

WIP until Murali gets around to adding metadata to the snapshot data, which is estimated to be live next month.

[klauer]

Going against what I said in the PR text, I don't think we really need Murali's archiver update to get this in.

It does work as-is, just does not contain all the metadata that we want in the get_snapshot response. I'll ask for a review and we'll go from there.

[ZLLentz]

Environment variable additions look good too! I forgot this was so hard-coded