i.gensigset: add test file

[jayneel-shah18]

This PR introduces a regression test suite for the i.gensigset module, designed to validate the statistical structure of the generated .sig files and verify the behavior of the maxsig parameter under different configurations.

Tests Added

• test_basic_signature_generation Ensures that a .sig file is correctly generated for a synthetic training map and that each signature includes well-formed mean vectors and statistically sound values.

• test_maxsig_parameter Verifies that increasing the maxsig parameter results in an equal or greater number of detected classes and subsignatures. Confirms the expected behavior of the Gaussian mixture model’s flexibility.

• test_minimal_maxsig Evaluates module behavior when maxsig=1, enforcing at most one subsignature per class. Ensures the total number of subsignatures remains within valid bounds and is consistent with the training map structure.

Looking forward to feedback and suggestions.