Fix spurious 0 complex part in Pauli evolution (backport #13643)

[mergify]

Summary

Fixes #13642.

Details and comments

This boils down to the fact that, x * (1+0j) = 1.0*x + 0.0*I but pre-1.3 we only multiplied by 1.

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This is an automatic backport of pull request #13643 done by [Mergify](https://mergify.com).

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[coveralls]

Pull Request Test Coverage Report for Build 12707553253

Details

• 8 of 10 (80.0%) changed or added relevant lines in 1 file are covered.
• 10 unchanged lines in 4 files lost coverage.
• Overall coverage increased (+0.004%) to 88.919%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
qiskit/synthesis/evolution/suzuki_trotter.py	8	10	80.0%

Files with Coverage Reduction	New Missed Lines	%
crates/accelerate/src/unitary_synthesis.rs	1	93.18%
crates/qasm2/src/expr.rs	1	94.02%
crates/qasm2/src/lex.rs	3	91.73%
qiskit/synthesis/evolution/product_formula.py	5	89.58%

Totals
Change from base Build 12707459091:	0.004%
Covered Lines:	79154
Relevant Lines:	89018

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💛 - Coveralls