Adds a function that constructs a Merkle proof for a generalized index.
This will be used during light client sync to update light clients with
a new state (see NEXT_SYNC_COMMITTEE_INDEX / FINALIZED_ROOT_INDEX).
* add merge SSZ consensus object tests
* add merge attestations, attester slashing, proposer slashing, and voluntary exit test fixtures
* throw catchable exception rather than assert on invalid SingleMemberUnion selector
* hash_tree_root can assert, because it's trusted data by that point
* re-assert on writing, since also trusted data
* beta.4 update
* implement upgrade_to_merge()
* add random tests and rename "Official" to "Ethereum Foundation"
* checkDir = true covers dirExists(...)
* invalidate CI EF fixtures cache
* more correct cache invalidation
* update to Altair as of v1.1.0-alpha.7
* introduce Altair types into attestation pool
* avoid allocating/copying pubkeys excessively in get_next_sync_committee()
* proposed structure for hf1
* refactor datatypes.nim into datatypes/{base, phase0, hf1}.nim
* hf1 is Altair
* some syncing with alpha 2
* adjust epoch processing to disambiguate access to RewardFlags
* relocate StateData to stay consistent with meaning phase 0 StateData
* passes v1.1.0 alpha 5 SSZ consensus object tests
* Altair block header test fixtures work
* fix slash_validator() so that Altair attester slashings, proposer slashings, and voluntary exit textures work
* deposit operation Altair test fixtures work
* slot sanity and all but a couple epoch transition tests switched to Altair
* attestation Altair test fixtures work
* Altair block sanity test fixtures work
* add working altair sync committee tests
* improve workarounds for sum-types-across-modules Nim bug; incorporate SignedBeaconBlock root reconstuction to SSZ byte reader
* update more spec refs in beacon_chain/spec/presets; skip skipped constant sanity checks also from markdown reports' perspectives
* mark skipped as skipped in markdown
* initial 0.11.1 spec commit; no test regressions and finalizes in eth2_network_simulation
* with BLS 0.10/0.11 available, stop skipping attester slashing, proposer slashing, and voluntary exist operations fixture tests
* switch param orders to group state.{fork, genesis_validators_root}; bump spec/datatypes spec version for network purposes
* mark attestation construction and broadcast and some minimal/mainnet constants as 0.11.1-compatible; remove phase 1 sharding constants from minimal which don't exist in that preset