Summary

Two pieces of infrastructure cleanup that were originally bundled with #85 but are independently useful:

1. Repoint the dead test-fixtures submodule. tests/integration/fixtures currently points at git@github.com:cwerling/PSPTool-fixtures.git, which returns "Repository not found" — almost certainly collateral from the LFS-quota recreations the commit log mentions. Anyone running git submodule update --init on a fresh checkout today fails immediately. Switching to git@github.com:PSPReverse/Test-PSPTool.git, which is the org's active firmware corpus (54 ROMs, AM4 / X399 / Naples era), restores submodule init.
2. Add scaffolding for an EPYC integration test. Layout shifts from fixtures/roms/ to fixtures/test_files/ to match the Test-PSPTool repo's flat layout, and TestZenGenerationBackfill is added to tests/integration/test_rom_files.py. It maps the 5 EPYC fixture filenames to expected Zen generations and asserts via _find_fixture + subTest. The class skips cleanly today (No EPYC fixtures present under tests/integration/fixtures/test_files) — it starts asserting only after Test-PSPTool gains the EPYC ROMs and the gitlink in this PR is bumped to a SHA that contains them.

Why this is its own PR

This work is a strict superset of "the submodule URL is dead." The integration-test class is dormant scaffolding until Test-PSPTool catches up, and bundling it with the back-fill in #85 muddies the review (one PR mixing fix-the-bug with fix-the-CI-corpus-pointer). Keeping them separate means:

• Detect zen_generation for single-generation EPYC BIOSes #85 reviewers focus on the back-fill on its merits — fully covered by unit tests, no submodule dependency.
• This PR reviewers focus on whether the move to PSPReverse/Test-PSPTool is the right destination, and whether the dormant test class shape is acceptable.
• Either can be merged before the other, in any order.

What's in the PR

Single commit:

• .gitmodules — URL change to git@github.com:PSPReverse/Test-PSPTool.git
• tests/integration/fixtures — gitlink moved to current Test-PSPTool master HEAD bca9c0e. Real commit, exists, has the existing 54-ROM corpus.
• tests/integration/test_rom_files.py — rom_fixtures_path updated to fixtures/test_files; new TestZenGenerationBackfill class.

Test plan

• Existing integration tests (TestRomFiles.*): runs against the new submodule pointer (Test-PSPTool master, 54 ROMs, AM4 / X399 / Naples era) — all pass, AM4 combo control X470D4U2-2T 3.40 keeps existing combo_dir output unchanged.
• TestZenGenerationBackfill: skips with the documented "No EPYC fixtures present" message, exactly as expected on this gitlink.

Follow-up

A companion change in PSPReverse/Test-PSPTool adds 5 EPYC fixture files (Rome / Milan / Genoa / Siena / Turin) under test_files/ and refreshes test_psptool.py for the current PSPTool API (it imports HeaderEntry and walks psp.blob.fets, both gone). Once that lands, a one-line gitlink bump in this repo flips TestZenGenerationBackfill from skip to assert.