* persist light client updates
* update beacon chain to serve light client updates
* resolve todos
* cache best update
* extend cache parts
* is better light client update
* resolve merge conflict
* initial api changes
* add lc update db column
* fmt
* added tests
* add sim
* Merge branch 'unstable' of https://github.com/sigp/lighthouse into persist-light-client-updates
* fix some weird issues with the simulator
* tests
* Merge branch 'unstable' of https://github.com/sigp/lighthouse into persist-light-client-updates
* test changes
* merge conflict
* testing
* started work on ef tests and some code clean up
* update tests
* linting
* noop pre altair, were still failing on electra though
* allow for zeroed light client header
* Merge branch 'unstable' of https://github.com/sigp/lighthouse into persist-light-client-updates
* merge unstable
* remove unwraps
* remove unwraps
* Update light_client_update.rs
* merge unstable
* move functionality to helper methods
* refactor is best update fn
* refactor is best update fn
* improve organization of light client server cache logic
* fork diget calc, and only spawn as many blcoks as we need for the lc update test
* fetch lc update from the cache if it exists
* fmt
* Fix beacon_chain tests
* Add debug code to update ranking_order ef test
* Fix compare code
* merge conflicts
* fix test
* Merge branch 'persist-light-client-updates' of https://github.com/eserilev/lighthouse into persist-light-client-updates
* Use blinded blocks for light client proofs
* fix ef test
* merge conflicts
* fix lc update check
* Lint
* resolve merge conflict
* Merge branch 'persist-light-client-updates' of https://github.com/eserilev/lighthouse into persist-light-client-updates
* revert basic sim
* small fix
* revert sim
* Review PR
* resolve merge conflicts
* Merge branch 'unstable' into persist-light-client-updates
## Issue Addressed
Resolves#2545
## Proposed Changes
Adds the long-overdue EF tests for fork choice. Although we had pretty good coverage via other implementations that closely followed our approach, it is nonetheless important for us to implement these tests too.
During testing I found that we were using a hard-coded `SAFE_SLOTS_TO_UPDATE_JUSTIFIED` value rather than one from the `ChainSpec`. This caused a failure during a minimal preset test. This doesn't represent a risk to mainnet or testnets, since the hard-coded value matched the mainnet preset.
## Failing Cases
There is one failing case which is presently marked as `SkippedKnownFailure`:
```
case 4 ("new_finalized_slot_is_justified_checkpoint_ancestor") from /home/paul/development/lighthouse/testing/ef_tests/consensus-spec-tests/tests/minimal/phase0/fork_choice/on_block/pyspec_tests/new_finalized_slot_is_justified_checkpoint_ancestor failed with NotEqual:
head check failed: Got Head { slot: Slot(40), root: 0x9183dbaed4191a862bd307d476e687277fc08469fc38618699863333487703e7 } | Expected Head { slot: Slot(24), root: 0x105b49b51bf7103c182aa58860b039550a89c05a4675992e2af703bd02c84570 }
```
This failure is due to #2741. It's not a particularly high priority issue at the moment, so we fix it after merging this PR.
## Proposed Changes
Update test vectors for v0.12.3, and introduced configurable `proportional_slashing_multiplier`.
Also makes `YamlConfig` a bit safer by making every field access in `apply_to_chain_spec` explicit, and removing the `#[serde(default)]` attribute, which would instantiate missing fields to type defaults! Risky!
