Warn when finalize_options() overrides a property explicitly set by the user

[TsafrirA]

Summary

This PR adds a warning when finalize_options() overrides a field which was explicitly set by the user. It uses the recent transition to pydantic models which allow the distinction between defaults and values explicitly set by the user.

AI/LLM disclosure

• I used the following tool to generate or modify code: IBM BOB

[TsafrirA]

@SamFerracin
I verified that legacy estimator silently overrides without erroring or warning, at least for this example:

estimator = EstimatorV2(backend)
estimator.options.resilience.pec_mitigation = True
estimator.options.twirling.enable_gates = False

The job runs and the metadata shows

 'twirling': {'enable_gates': True,
  'enable_measure': True,
  'num_randomizations': 'auto',
  'shots_per_randomization': 'auto',
  'interleave_randomizations': True,
  'strategy': 'active-accum'},