Division by 0 in `test_multivariate_simulation_2D`

[jpaillard]

The test computes an estimated signal-to-noise ratio in a scenario where the SNR is set to np.inf, resulting in a division by 0 that sometimes pops up in the tests:

hidimstat/test/_utils/test_scenario.py

Line 50 in 01d12f9

signal_noise_ratio_hat = np.linalg.norm(y - noise) / np.linalg.norm(noise)

See, for instance, https://github.com/mind-inria/hidimstat/actions/runs/17578598386/job/49929539204?pr=355

I'm not sure why this does not happen systematically though 🤔

[bthirion]

We can always regularize variance estimates so that they are nonzero.