Fix/commuting2q block parameter preservation

[TalKozlovski]

This PR fixes parameter loss in Commuting2qBlock where params was hardcoded to an empty list, breaking parametric circuits.

Fix issue #16456

Details

Problem: Commuting2qBlock.__init__ hardcoded params=[], losing all parameters from input gates.

Solution: Extract parameters from gate operations.

Changes:

• Modified __init__ to collect parameters from ParameterExpression objects
• Added two tests in test_swap_strategy_router.py

AI/LLM disclosure

• I didn't use LLM tooling, or only used it privately.
• I used the following tool to help write this PR description: IBM Bob
• I used the following tool to generate or modify code: IBM Bob

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All committers have signed the CLA.

[ShellyGarion]

Thanks @TalKozlovski for finding and fixing the issue!
Could you also add a bug-fix release note to your PR?

[Cryoris]

Thanks for the contribution -- this needs a bit more testing to ensure the parameters also handled correctly in a circuit context. I left some comments below.

[Cryoris]

Can we add tests where

• we check the circuit containing the Commuting2qBlock also knows about the parameters, and
• we assign parameters to a circuit containing Commuting2qBlock -- especially with an example where we re-use the same parameter multiple times inside a block

This is to ensure that not only the block knows about the parameters but that they are also handled correctly

[TalKozlovski]

Thank you for the suggestions, added respective tests

[Cryoris]

The parameters should support unique sorting already, which will take into account indices of parameters coming from a ParameterVector. Sorting by name will produce unexpected sortings like v[0], v[1], v[10], v[2], v[3], ....

[TalKozlovski]

I drop the sorting and just convert the set into a list

[Cryoris]

Dropping the sorting seems correct since the block does not need to know anything about parameter order -- the circuit will figure out the right order when assigning parameters by array. But you have a test which asserts that the order is what you expect, we have to remove this test if we no longer sort.

[Cryoris]

This contains only Parameters, not expressions

Suggested change

	params_set: set[ParameterExpression] = set()
	params_set: set[Parameter] = set()