Update LCFS, WAS, and ETB private prerequisites

[MaxGhenis]

Context

After the FRS 2024-25 update, the remaining non-SPI private UKDS prerequisites are still stale in the data build:

• LCFS: repo uses lcfs_2021_22.zip; UKDS has Living Costs and Food Survey 2023-2024, SN 9468, DOI 10.5255/UKDA-SN-9468-3.
• WAS: repo uses was_2006_20.zip / Round 7; UKDS has Wealth and Assets Survey Waves 1-5 and Rounds 5-8, 2006-2022, SN 7215, DOI 10.5255/UKDA-SN-7215-20.
• ETB: repo uses etb_1977_21.zip; UKDS has Effects of Taxes and Benefits on Household Income, 1977-2024, SN 8856, DOI 10.5255/UKDA-SN-8856-4.

SPI is deliberately excluded here because spi_2022_23.zip is already in policyengine/policyengine-uk-data-private and can be switched separately.

Proposed work

• Fetch the restricted UKDS tab zips for SN 9468, SN 7215, and SN 8856.
• Upload them to policyengine/policyengine-uk-data-private with release-year names.
• Replace hard-coded folders and filenames in LCFS, WAS, and ETB ingestion with release metadata.
• Rebuild or invalidate cached QRF model files where the source release changes.
• Add tests that fail if the code points at stale UKDS releases.

Notes

This likely needs more than filename bumps:

• LCFS has year-specific tab filenames and fuel-price source-year constants.
• WAS Round 8 has new household/person files and should be checked against the Round 7 variable mapping.
• ETB 2023-24 should advance DEFAULT_ETB_YEAR and the household tab filename after validating the VAT columns.

[MaxGhenis]

Resolved by #413, which updated LCFS to 2023-24, WAS to Round 8 / 2006-2022, and ETB to 1977-2024 private prerequisites, added release metadata/tests, and passed current CI before merge.