Refactoring API structure

[d1ssk]

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• Make sure you have tests for the new code and that test passes (run tox)
• format added code by black -l 120 <filename>
• If applicable, add a line to the [unreleased] part of CHANGELOG.md, following keep-a-changelog.

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Context (if applicable):
This PR aligns with the refactored backend interface structure introduced in graphix PR /#261

Description of the change:

• Implemented IBMQBackend, a concrete subclass of graphix.interface.MBQCBackend
• Implemented IBMQJobHandler as a subclass of graphix.interface.JobHandler
• Refactored and separated concerns:
  • compiler.py: converts Pattern to QuantumCircuit
  • executor.py: handles both real hardware execution and Aer simulation
  • job_handler.py: manages job status and ID
  • result_utils.py: extracts and formats output from raw IBMQ results
  • compile_options.py: defines IBMQCompileOptions dataclass for type-safe parameter handling
• backend.py: orchestrates the entire workflow from compile → submit → retrieve

Related issue:

also see that checks (github actions) pass.
If lint check keeps failing, try installing black==22.8.0 as behavior seems to vary across versions.