fwk: rename package testdata to internal/fwktest

[dolmen]

Fixes #941 .

1st commit:

$ mkdir -p fwk/internal/fwktest
$ git mv fwk/testdata/*.go fwk/internal/fwktest
$ ( cd fwk/internal/fwktest; sed -i '' 's/package testdata/package fwktest/' *.go )
$ git add fwk/internal/fwktest

2nd commit:

$ ( cd fwk; find . -name '*.go' -exec grep -Hq 'fwk/testdata' '{}' \; -print | xargs sed -i '' -e 's!fwk/testdata!fwk/internal/fwktest!' -e 's!testdata\.!fwktest.!' -e 's!some tools defined in testdata!some tools defined in fwktest!' )
$ git add fwk

[sbinet]

LGTM.

thanks for cleaning that up.

like for the other pending PRs, please send another (just one) pull request against the go-hep/license repository, adding yourself to the AUTHORS and/or CONTRIBUTORS file(s).
then I'll be able to collect and merge all your other pull requests.
(I can't do that before you've added yourself to the list of authors/contributors of the Go-HEP project)

thanks.

[sbinet]

ah. one finnicky import ordering that doesn't suit gofmt (or goimport in this case).

[sbinet]

I'll handle the staticcheck failure.

thanks.