feat: Added cost_confidence API on jobs, hugr and qir

[qfreewilll]

Output of the integration tests. The new warnings for the old cost() endpoints are visible for qir and hugr. There was no test for jobs.cost() and I didn't add one.

uv run pytest -vsn 0 -ra --reruns=0 integration/test_jobs.py integration/test_qir.py integration/test_qsys_jobs.py -k 'test_job_cost_confidence or test_qir_cost or test_hugr_cost or test_hugr_costing or test_costing_qir_on_NG_devices'

integration/test_qsys_jobs.py::test_hugr_costing PASSED
integration/test_qsys_jobs.py::test_hugr_cost_confidence PASSED
integration/test_qir.py::test_costing_qir_on_NG_devices PASSED
integration/test_qir.py::test_qir_cost_confidence PASSED
integration/test_jobs.py::test_job_cost_confidence
PASSED

================ warnings summary ================
integration/test_qsys_jobs.py::test_hugr_costing
  /Users/will.angenent/qnexus/qnexus/client/hugr.py:291: DeprecationWarning: hugr.cost() is deprecated. Please update to use hugr.cost_confidence() instead.
    warnings.warn(

integration/test_qsys_jobs.py: 4 warnings
integration/test_qir.py: 4 warnings
integration/test_jobs.py: 2 warnings
  /Users/will.angenent/qnexus/.venv/lib/python3.12/site-packages/quantinuum_schemas/models/backend_config.py:262: DeprecationWarning: QuantinuumConfig is deprecated for submission to Helios systems and support will be removed in a future release. Please use HeliosConfig instead.
    warnings.warn(

integration/test_qir.py::test_costing_qir_on_NG_devices
  /Users/will.angenent/qnexus/qnexus/client/qir.py:270: DeprecationWarning: qir.cost() is deprecated. Please update to use qir.cost_confidence() instead.
    warnings.warn(

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
=========================================================================================== 5 passed, 23 deselected, 12 warnings in 28.01s ===========================================================================================

[vanyae-cqc]

Looks good! Shared some thoughts but let me know if anything doesn't make sense