Fix parameter handling for NLocal(..., flatten=True) and standard gates (backport #13482)

[mergify]

Summary

Fixes #13478.

The fast-path for parameterizing standard gates caused an inconsistent state of the circuit, which is now fixed by using the explicit circuit._append_standard_gate method.

Details and comments

I'm not 100% sure what exactly the inconsistency was. Another way to fix this issue was to have the Rust-side assign_parameter_inner to explicitly re-assign the params attribute of the cached Python gate. So I'm assuming the old path didn't correctly register the gate in the cache, but I couldn't pin point the exact location in the code. If someone has more insight that would be great to know 🙂

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This is an automatic backport of pull request #13482 done by [Mergify](https://mergify.com).

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[coveralls]

Pull Request Test Coverage Report for Build 12038616619

Details

• 7 of 7 (100.0%) changed or added relevant lines in 1 file are covered.
• 4 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.02%) to 88.934%

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Files with Coverage Reduction	New Missed Lines	%
crates/qasm2/src/lex.rs	4	92.98%

Totals
Change from base Build 12027471253:	0.02%
Covered Lines:	79071
Relevant Lines:	88910

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💛 - Coveralls