🧪 Add tests for CSimulator simulator property

[akutuva21]

🎯 What: The testing gap in bionetgen/simulator/csimulator.py:224 for the CSimulator.simulator property (getter and setter) has been addressed. The logic inside the setter validates initial species counts and parses/filters numeric parameters before initializing CSimWrapper.

📊 Coverage: The new tests cover:

1. The happy path for simulator setter: Mocking valid, ignored (starting with _), and non-float evaluating parameters to test the filtering, and mocking initial species count, validating CSimWrapper is instantiated with the correct num_params and num_spec_init.
2. The getter property returning the mocked _simulator.
3. Error handling: Explicitly raising BNGCompileError when CSimWrapper raises an exception during initialization.

✨ Result: Test coverage for bionetgen/simulator/csimulator.py is improved, increasing confidence in the CSimulator wrapper logic.

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PR created automatically by Jules for task 6771044870234571453 started by @akutuva21

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