Feat: added proof-of-concept of otv consensus

packages/unbreakable_consensus/otv/approvers.go

packages/unbreakable_consensus/otv/approvers_database.go

packages/unbreakable_consensus/otv/conflict_set.go

packages/unbreakable_consensus/otv/elder_mask.go

packages/unbreakable_consensus/otv/node.go

packages/unbreakable_consensus/otv/node_events.go

packages/unbreakable_consensus/otv/otv_test.go

packages/unbreakable_consensus/otv/reality.go

packages/unbreakable_consensus/otv/solidifier.go

packages/unbreakable_consensus/otv/tip_selector.go

packages/unbreakable_consensus/otv/transaction.go

packages/unbreakable_consensus/otv/transaction_database.go

packages/unbreakable_consensus/otv/transaction_metadata.go