Make disable_time_zone_synchronization idempotent

[omolenkamp]

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[CLAassistant]

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[chelnak]

Hey @omolenkamp, thanks for the contribution!

Please could you provide a little more context around this change?

Also it would be great if you could add a test or two for the new functionality.

Let us know if you need any help.

[omolenkamp]

disable_time_zone_synchronization works by setting StartBoundary to a local timestamp (no zone offset) when true, and using a timestamp including a zone offset when false. Because of this, the current value of disable_time_zone_synchronization can be determined by testing if StartBoundary includes a zone offset. (Z, +xx:xx, or -xx:xx)

(start_boundary cannot be used here, as the Ruby Time class doesn't differentiate between local and zoned timestamps)

[chelnak]

Hey @omolenkamp, thanks for updating this PR.

There were a few spec failures. I've fixed these to help move things along. If our CI passes I'll get this merged.