add atol parameter to SparsePauliOp.equiv

[kevinsung]

Summary

Adds atol parameter to SparsePauliOp.equiv.

Details and comments

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[coveralls]

Pull Request Test Coverage Report for Build 2617177950

• 5 of 5 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.0005%) to 84.004%

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Totals
Change from base Build 2611640146:	0.0005%
Covered Lines:	55825
Relevant Lines:	66455

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💛 - Coveralls

[Cryoris]

LGTM 👍🏻 this also doesn't change the default behavior since NumPy's default for atol is 1e-8 which is the same as the tolerances mixin now provides as default.

I'll hold off automerge to give others a chance to review, maybe @chriseclectic or @ikkoham have an opinion here!

[t-imamichi]

Thanks. Looks good.