Round durations in GenericBackendV2 (backport #11780)

[mergify]

Summary

This PR makes sure that the conversion of GenericBackendV2 instruction durations to dt is exact to avoid user warnings during scheduling of type:

UserWarning: Duration is rounded to 616 [dt] = 1.367520e-07 [s] from 1.366887e-07 [s]

Given that the durations are sampled randomly, and the rounded duration is the one used in the scheduling passes, we might as well make sure in advance that the conversion from seconds to dt will be exact and doesn't raise warnings.

Details and comments

I am not sure this qualifies as a bugfix but I think it improves the readability of the test logs. For example, for test_scheduling_backend_v2 in test/python/compiler/test_transpiler.py. Before:

/Users/ept/qiskit_workspace/qiskit/qiskit/circuit/duration.py:37: UserWarning: Duration is rounded to 986 [dt] = 2.188920e-07 [s] from 2.189841e-07 [s]
  warnings.warn(
/Users/ept/qiskit_workspace/qiskit/qiskit/circuit/duration.py:37: UserWarning: Duration is rounded to 2740 [dt] = 6.082800e-07 [s] from 6.083383e-07 [s]
  warnings.warn(
/Users/ept/qiskit_workspace/qiskit/qiskit/circuit/duration.py:37: UserWarning: Duration is rounded to 2697 [dt] = 5.987340e-07 [s] from 5.988312e-07 [s]
  warnings.warn(
/Users/ept/qiskit_workspace/qiskit/qiskit/circuit/duration.py:37: UserWarning: Duration is rounded to 178 [dt] = 3.951600e-08 [s] from 3.956636e-08 [s]
  warnings.warn(
.
----------------------------------------------------------------------
Ran 1 test in 0.548s

OK

After:

.
----------------------------------------------------------------------
Ran 1 test in 0.506s

OK

---

This is an automatic backport of pull request #11780 done by [Mergify](https://mergify.com).

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[coveralls]

Pull Request Test Coverage Report for Build 8423731036

Details

• 4 of 4 (100.0%) changed or added relevant lines in 1 file are covered.
• 22 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.03%) to 89.285%

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Files with Coverage Reduction	New Missed Lines	%
crates/qasm2/src/lex.rs	4	91.6%
crates/qasm2/src/parse.rs	18	96.69%

Totals
Change from base Build 8421244435:	-0.03%
Covered Lines:	58888
Relevant Lines:	65955

---

💛 - Coveralls