* pallet-beefy: ensure mandatory block once per session

Signed-off-by: acatangiu <[email protected]>

* pallet-beefy: fix tests with auth changes every session

Signed-off-by: acatangiu <[email protected]>

* Apply suggestions from code review

Co-authored-by: André Silva <[email protected]>

* beefy: fix incorrect skip session metric on node restart

Co-authored-by: André Silva <[email protected]>