feat(gam): close general-family multismooth surfaces

[Ananyapam7]

Summary

• exercise and verify wrapped multi-smooth Sl blocks across both predictors of an mgcv::gaulss model
• align public parametric and smooth labels with mgcv formula-list predictor suffixes across summary, ANOVA, diagnostics, plots, derivatives, snapshots, and gam.vcomp
• add vendored-mgcv fixtures covering smoothing selection, sp.vcov, one-SE selection, covariance variants, likelihood criteria, inference, residuals, concurvity, and k.check

Upstream parity anchors

• mgcv::gam, gam.setup.list, Sl.setup, Sl.initial.repara
• summary.gam, anova.gam, sp.vcov, one.se.rule, gam.vcomp
• concurvity, k.check, residuals.gam

Verification

• ruff check nampy/gam tests/families/test_general_family_mgcv_parity.py tests/optimization/test_mgcv_general_family_preoptimization_parity.py tests/parity/test_mgcv_general_family_prediction_filters_parity.py tests/parity/test_mgcv_snapshot_extended_matrix.py
• git diff --check
• affected suite: 93 passed, 66 deselected
• final exact-node rerun: wrapped-block setup 1 passed; comprehensive snapshot 1 passed; prediction filters/labels 8 passed

Remaining scope

Wave 1 is complete after this subwave. Remaining planned work is the bounded Wave 2 basis-family sequence (cp, bs, ds, gp, mrf, sos).