Move the SCF wealth stage (net worth, liquid assets, auto loans) to the 2025 SCF #1358

Follow-up to #1073 and #1246. #1246 imputes education debt from the 2025 SCF, while net worth, the liquid-asset leaves and auto loans still read the 2022 files. Measures that combine debt with wealth (the payment as a share of net worth, liquid assets left after a month's payment, and median net worth before and after payments) then mix two survey waves in one household. Moving the whole scf_wealth stage to 2025 puts them on one wave.

This changes every US build that runs the SCF wealth stage, not only the student debt pilot's, so it goes through the usual release review.

Steps (from #1246's scope note)

• Point fetch_scf_2022_summary_extract and fetch_scf_2022_full_extract (and their load_* callers) at SCF_2025_SUMMARY_EXTRACT and SCF_2025_FULL_EXTRACT, using fetch_scf_public_file.
• Drop the two 2022 artifacts from source_stages.json and repoint the scf_2022 vintage.
• Re-check the net-worth and asset plausibility bands, then re-derive the frozen digest and the spec-engine identity values, as Impute federal student loan balances from the 2025 SCF (#1073) #1246 does.

According to #1246, the predictor and target code needs no change. The 2025 summary extract carries every column the shared predictor construction reads (age, hhsex, racecl5, married, kids, wageinc, intdivinc, ssretinc, plus liq, stocks, nmmf, bond, networth), and the 2025 codebook still lists the auto-loan items. racecl5 and racecl4 fold the new Middle Eastern or North African category into White non-Hispanic.

Done when

• The SCF wealth stage reads only the 2025 files.
• A before/after table compares net worth, liquid assets and auto loans with the 2025 SCF's published figures.
• The plausibility bands are rechecked, and the digest and identity values are re-derived.