ERA: Add ERA file support package

[ScottyPoi]

Introduces new package "@ethereumjs/era"

Package will include utility functions to enable creation and parsing of ERA files (era, era1, era2, etc.)

• era/src/types.ts
  • types for era data
• era/src/snappy.ts
  • functions for compressing / decompressing era file data
• era/src/e2store.ts
  • functions for encoding / decoding e2store objects
• era/src/blockTuple.ts`
  • functions to serialize / deserialize block "tuples"
• era/src/era1.ts`
  • functions to create / read era1 files

ERA1

era1 specs: ethereum/go-ethereum#26621

Era1 stores one epoch of history data along with the hash tree root of the epoch accumulator as an anchor for validation.

Era1 contains 8192 block tuples

A block tuple contains

• header
• body
• block receipts
• total difficulty

Era1 also contains the root of an Epoch Accumulator

Epoch Accumulator is an SSZ object used in Portal Network. An Epoch Accumulator is constructed from a list of 8192 Header Records

A Header Record is an object with a blockHash and totalDifficulty.

The accumulator can be reconstructed to validate the contents of era1 against the provided accumulator root.

The accumulator roots are part of a static set of roots that can be externally validated.

Client - @ethereumjs/client

• Imports new era package.
• Adds a new non-standard RPC method debug_exportHIstory which triggers a client to export its history to era1 files

[codecov]

Codecov Report

Attention: Patch coverage is 14.47368% with 65 lines in your changes missing coverage. Please review.

Project coverage is 75.20%. Comparing base (4ed3482) to head (daa1850).

Additional details and impacted files

Flag	Coverage Δ
block	76.87% <ø> (ø)
blockchain	85.69% <ø> (ø)
client	66.01% <14.47%> (-0.26%)	⬇️
common	90.31% <ø> (ø)
devp2p	76.27% <ø> (ø)
ethash	81.04% <ø> (ø)
evm	69.34% <ø> (ø)
genesis	99.84% <ø> (ø)
mpt	59.92% <ø> (-0.04%)	⬇️
rlp	69.70% <ø> (ø)
statemanager	70.15% <ø> (ø)
tx	80.52% <ø> (ø)
util	77.51% <ø> (ø)
vm	57.81% <ø> (ø)
wallet	83.78% <ø> (ø)

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