🧪 [Test Improvement] Add coverage for _replace_parameters_brackets repl function

[akutuva21]

🎯 What:
The inner function repl of _replace_parameters_brackets in bionetgen/modelapi/sympy_odes.py was previously untested. This function is responsible for regex replacements of array-like parameter references in mathematical expressions, handling both standard replacements and gracefully failing back to p{idx} for out-of-bounds parameter references.

📊 Coverage:
Added a new unit test, test_replace_parameters_brackets in tests/test_sympy_odes.py. This test fully covers:

• Normal parameter string replacements where indices are within bounds.
• Out of bounds index replacements (the edge case repl handles explicitly).
• Varying whitespace within the brackets.
• No matches strings to ensure they are returned unchanged.
• An empty parameter list.

✨ Result:
The test suite now properly covers the parameter replacement logic, catching potential future bugs and ensuring robust and deterministic regex functionality for parsing mathematical equations. All tests, including the full suite run, pass successfully without regressions.

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PR created automatically by Jules for task 9136984088447531084 started by @akutuva21

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