test: Add a unit test for the usage of restrict_to and restriction_idx_key in select_in_dataset of GoldSelector - #322

Closes #310

• select_in_dataset forwards restrict_to and restriction_idx_key to select_in_table, but neither parameter had dedicated unit test coverage in this file (only indirectly exercised via GoldSplitter).

Tests added

• test_select_in_dataset_with_restrict_to — verifies selection is limited to the idx_vector values passed in restrict_to, not the full dataset.

• test_select_in_dataset_with_restriction_idx_key — verifies filtering happens on a custom key (idx) instead of the default idx_vector, and that idx/idx_vector mapping stays correct for selected samples.

• test_select_in_dataset_with_restrict_to_exceeding_size — verifies a ValueError is raised when select_size exceeds the size of the restricted pool (not the full dataset).

• All 61 tests in tests/test_select.py pass.

Summary by cubic

Adds unit test coverage for restrict_to and restriction_idx_key in GoldSelector.select_in_dataset and select_in_table, closing #310.

• Verifies selection is limited to the passed restrict_to pool rather than the full dataset for both methods.
• Verifies filtering works on a custom restriction_idx_key and keeps the idx/idx_vector mapping correct for selected samples.
• Verifies a ValueError is raised when select_size exceeds the restricted pool size.
• Confirms select_in_table preserves the full source table while marking only the restricted pool.
• Updates are test-only; all 61 tests in tests/test_select.py pass.

^{Written for commit 77a0d7c. Summary will update on new commits.}