🧹 Refactor SpecializedModuleBackend to inherit from OptionalModuleBackend

[edithatogo]

🎯 What: SpecializedModuleBackend was a near-exact duplicate of OptionalModuleBackend, duplicating the dataclass properties, capabilities() definition, and is_available() method.
💡 Why: Having these redundant classes increases the maintenance burden. Extracting the common logic to inherit from the existing OptionalModuleBackend improves maintainability without altering existing functionality.
✅ Verification: Ran uv run pytest tests/test_specialized_accelerator_backends.py and the full test suite; no functionality is broken. Pre-commit hooks passed.
✨ Result: Cleaned up code duplication in pymars/specialized_accelerator_backends.py.

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PR created automatically by Jules for task 5140827773278103740 started by @edithatogo

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