Make pytest random inputs deterministic

[chenzc24]

Part of the follow-up work for #36.

Summary:

• Replace unseeded/global NumPy random calls in unit tests with local np.random.default_rng(...) instances.
• Keep existing assertions, tolerances, and product code unchanged.
• Remove one unused seed parameter from a deterministic test helper.

Tests:

• uv run --with pytest pytest tests/unit/calibration -q
• uv run --with pytest pytest tests/unit/aout -q
• uv run --with pytest pytest tests/unit/spectrum -q
• uv run --with pytest pytest tests/unit/dout/test_plot_residual_scatter.py tests/unit/fundamentals/test_verify_fit_sine_4param.py tests/unit/oversampling/test_matlab_compat_api.py -q
• uv run --with pytest pytest tests/unit/calibration tests/unit/aout tests/unit/spectrum tests/unit/dout/test_plot_residual_scatter.py tests/unit/fundamentals/test_verify_fit_sine_4param.py tests/unit/oversampling/test_matlab_compat_api.py -q

[Arcadia-1]

Closing as superseded by #48, which was squash-merged into main and includes this stack layer's deterministic RNG changes.