Merge #16931: test: add unittests for CheckProofOfWork

Summary:
0cc7dd74e0af735dddf7e786f4ed136c382a4ad5 test: add unittests for CheckProofOfWork (soroosh-sdi)

Pull request description:

following situations are covered:
- negative target
- overflow target
- target easier then powLimit
- invalid hash (hash > target)

Backport of Core PR16931

Test Plan: ninja check

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7995