support gate powering with **

[kevinsung]

Summary

Fixes #7473

Details and comments

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[coveralls]

Pull Request Test Coverage Report for Build 3892541916

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• 5 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.04%) to 84.642%

---

Files with Coverage Reduction	New Missed Lines	%
src/sabre_swap/layer.rs	2	98.95%
qiskit/pulse/library/waveform.py	3	91.49%

Totals
Change from base Build 3892057177:	0.04%
Covered Lines:	64481
Relevant Lines:	76181

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💛 - Coveralls

[jakelishman]

I'm happy to add this as a convenience magic method, especially given that the power function already exists. I think we ought to avoid modifying tests of other behaviour when adding the functionality, though - it's pretty minor here, but in general, changes to existing tests when a new feature is added usually indicates that some public-facing semantics changed, which is something we don't want.

[kevinsung]

Anything else?

[jakelishman]

Looks good, thanks!

[jakelishman]

Now with the merge conflict fixed.