Migrate to EstimatorV2 in tests

[garrison]

Partially addresses #506.

[coveralls]

Pull Request Test Coverage Report for Build 9995759082

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Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 9980490655:	0.0%
Covered Lines:	2410
Relevant Lines:	2410

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💛 - Coveralls

[garrison]

I made it so all the observables have trivial phase. As I mentioned in e8dd340:

The previous code passed observables_nophase to the cutting code, so it wasn't even testing the phases through the workflow. The correct way to handle such observables with nontrivial phase is to use the utility introduced in #587.

[ibrahim-shehzad]

This looks good to me, thanks!