The github.com/ethereum/go-verkle string remained only in vendor-
attribution comments (verkle/ files were vendored, not imported);
keeping the phantom require with version 00010101000000-000000000000
made the module unbuildable standalone. luxfi/crypto/ipa v1.2.4 was
an outdated indirect referencing this module's own ipa/ subdir,
causing ambiguous-import on standalone builds.
Both removed; module now builds with GOWORK=off GOFLAGS=-mod=mod.
Vendor-attribution comments in verkle/*.go retained.