`as_of=Timestamp(...)` searches in snapshots

[qc00]

Describe the bug

Any operation (read, etc.) that accepts Timestamp as a way to locate a version will currently search through all the snapshots if there are no live versions available.

This is probably for backwards compatibility with Arctic Python, but it is slow.

This feature is probably unexpected for external users, so we should hide it behind a library option that's enabled for internal users only.

[mehertz]

Removed and is not reliable. Not aware of any isues regarding that.