`go help clean` says:
The -fuzzcache flag causes clean to remove files stored in the Go build
cache for fuzz testing. The fuzzing engine caches files that expand
code coverage, so removing them may make fuzzing less effective until
new inputs are found that provide the same coverage. These files are
distinct from those stored in testdata directory; clean does not remove
those files.
What's the difference between the fuzz cache in the testdata/fuzz directory in your own package, and this "Go build cache for fuzz testing"? Is it duplicating testdata/fuzz per package? And where is it?