By: ValentinHirschi <valentin.hirschi@gmail.com>
validate retained four-loop parent routing Reuse the existing exact signed K6 witness validator and exercise all 19 registered four-loop classes without enabling unshipped artifacts. Focused gates: 23 native library tests and 16 K6 pipeline tests pass; one existing offline catalog comparison remains ignored. Format, check, Clippy and independent audit pass. User request: Ok, then now try and do the same for four loops! Start with trying to generate the closing set of IBPs for four-loop single scale vacuum integrals (0-scale really once using dimensional analysis to normalize that one scale to 1). The idea is then to be able to plug in this closing set of parametric IBPs into vakint and thus have the FORM-less "RustRed" reduction approach of `vakint` be able to reproduce end-to-end all 4-loop numerical tests there (which currently uses `FMFT`).