Implement Approval Voting Subsystem (#2112)

* skeleton

* skeleton aux-schema module

* start approval types

* start aux schema with aux store

* doc

* finish basic types

* start approval types

* doc

* finish basic types

* write out schema types

* add debug and codec impls to approval types

* add debug and codec impls to approval types

also add some key computation

* add debug and codec impls to approval types

* getters for block and candidate entries

* grumbles

* remove unused AssignmentId

* load_decode utility

* implement DB clearing

* function for adding new block entry to aux store

* start `canonicalize` implementation

* more skeleton

* finish implementing canonicalize

* tag TODO

* implement a test AuxStore

* add allow(unused)

* basic loading and deleting test

* block_entry test function

* add a test for `add_block_entry`

* ensure range is exclusive at end

* test clear()

* test that add_block sets children

* add a test for canonicalize

* extract Pre-digest from header

* utilities for extracting RelayVRFStory from the header-chain

* add approval voting message types

* approval distribution message type

* subsystem skeleton

* state struct

* add futures-timer

* prepare service for babe slot duration

* more skeleton

* better integrate AuxStore

* RelayVRF -> RelayVRFStory

* canonicalize

* implement some tick functionality

* guide: tweaks

* check_approval

* more tweaks and helpers

* guide: add core index to candidate event

* primitives: add core index to candidate event

* runtime: add core index to candidate events

* head handling (session window)

* implement `determine_new_blocks`

* add TODO

* change error type on functions

* compute RelayVRFModulo assignments

* compute RelayVRFDelay assignments

* fix delay tranche calc

* assignment checking

* pluralize

* some dummy code for fetching assignments

* guide: add babe epoch runtime API

* implement a current_epoch() runtime API

* compute assignments

* candidate events get backing group

* import blocks and assignments into DB

* push block approval meta

* add message types, no overseer integration yet

* notify approval distribution of new blocks

* refactor import into separate functions

* impl tranches_to_approve

* guide: improve function signatures

* guide: remove Tick from ApprovalEntry

* trigger and broadcast assignment

* most of approval launching

* remove byteorder crate

* load blocks back to finality, except on startup

* check unchecked assignments

* add claimed core to approval voting message

* fix checks

* assign only to backing group

* remove import_checked_assignment from guide

* newline

* import assignments

* abstract out a bit

* check and import approvals

* check full approvals from assignment import too

* comment

* create a Transaction utility

* must_use

* use transaction in `check_full_approvals`

* wire up wakeups

* add Ord to CandidateHash

* wakeup refactoring

* return candidate info from add_block_entry

* schedule wakeups

* background task: do candidate validation

* forward candidate validation requests

* issue approval votes when requested

* clean up a couple TODOs

* fix up session caching

* clean up last unimplemented!() items

* fix remaining warnings

* remove TODO

* implement handle_approved_ancestor

* update Cargo.lock

* fix runtime API tests

* guide: cleanup assignment checking

* use claimed candidate index instead of core

* extract time to a trait

* tests module

* write a mock clock for testing

* allow swapping out the clock

* make abstract over assignment criteria

* add some skeleton tests and simplify params

* fix backing group check

* do backing group check inside check_assignment_cert

* write some empty test functions to implement

* add a test for non-backing

* test that produced checks pass

* some empty test ideas

* runtime/inclusion: remove outdated TODO

* fix compilation

* av-store: fix tests

* dummy cert

* criteria tests

* move `TestStore` to main tests file

* fix unused warning

* test harness beginnings

* resolve slots renaming fallout

* more compilation fixes

* wip: extract pure data into a separate module

* wip: extract pure data into a separate module

* move types completely to v1

* add persisted_entries

* add conversion trait impls

* clean up some warnings

* extract import logic to own module

* schedule wakeups

* experiment with Actions

* uncomment approval-checking

* separate module for approval checking utilities

* port more code to use actions

* get approval pipeline using actions

* all logic is uncommented

* main loop processes actions

* all loop logic uncommented

* separate function for handling actions

* remove last unimplemented item

* clean up warnings

* State gives read-only access to underlying DB

* tests for approval checking

* tests for approval criteria

* skeleton test module for import

* list of import tests to do

* some test glue code

* test reject bad assignment

* test slot too far in future

* test reject assignment with unknown candidate

* remove loads_blocks tests

* determine_new_blocks back to finalized & harness

* more coverage for determining new blocks

* make `imported_block_info` have less reliance on State

* candidate_info tests

* tests for session caching

* remove println

* extricate DB and main TestStores

* rewrite approval checking logic to counteract early delays

* move state out of function

* update approval-checking tests

* tweak wakeups & scheduling logic

* rename check_full_approvals

* test that assignment import updates candidate

* some approval import tests

* some tests for check_and_apply_approval

* add 'full' qualifier to avoid confusion

* extract should-trigger logic to separate function

* some tests for all triggering

* tests for when we trigger assignments

* test wakeups

* add block utilities for testing

* some more tests for approval updates

* approved_ancestor tests

* new action type for launch approval

* process-wakeup tests

* clean up some warnings

* fix in_future test

* approval checking tests

* tighten up too-far-in-future

* special-case genesis when caching sessions

* fix bitfield len

Co-authored-by: Andronik Ordian <write@reusable.software>