go-bip39 is gone from GitHub, so keyfunc now carries the part of
v1.1.0 it uses, with the upstream LICENSE beside it, and imports it
from internal/bip39. Upstream's tests and test vectors for the kept
code come along unchanged.
Changes beyond the trimming are what the linter asked for: the
package-level variables moved into the functions that use them, three
error strings were lower-cased, and the unknown-word error now wraps
ErrInvalidMnemonic.
go.mod no longer requires go-bip39. go mod tidy keeps its two go.sum
lines, because a test in sneak/secret's bip85 package imports it, and
drops five lines that only go-bip39's own requirements needed.
Model: opus-5-5
