Add era file support

[acolytec3]

This adds support for the era format which contains SignedBeaconBlock and BeaconState objects.

Note, this currently only support era files from deneb and later since the underlying SSZ types from micro-eth-signer are limited to deneb types.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.87%. Comparing base (8630cc8) to head (4c87e9e).
Report is 1 commits behind head on master.

Additional details and impacted files

Flag	Coverage Δ
block	76.87% <ø> (ø)
blockchain	85.69% <ø> (ø)
client	66.26% <ø> (-0.02%)	⬇️
common	90.73% <ø> (ø)
devp2p	76.27% <ø> (ø)
ethash	81.04% <ø> (ø)
evm	71.04% <ø> (ø)
genesis	99.84% <ø> (ø)
mpt	59.72% <ø> (ø)
rlp	69.70% <ø> (ø)
statemanager	70.47% <ø> (ø)
tx	80.96% <ø> (ø)
util	85.54% <ø> (ø)
vm	57.81% <ø> (ø)
wallet	83.78% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

[ScottyPoi]

LGTM. Can confirm this works with post-deneb era files.

Approving with a TODO to fill in the missing ssz types, either after an update from micro-eth-signer or manually here in the era package

[ScottyPoi]

This can be tested with a simple script like:

const file = await fetch('https://mainnet.era.nimbus.team/mainnet-01340-429201f5.era')
const fileBytes = new Uint8Array(await file.arrayBuffer())

const blocks = readBlocksFromEra(fileBytes)
for await (const block of blocks) {
    console.log(block)
}