* all: implement era format, add history importer/export
* internal/era/e2store: refactor e2store to provide ReadAt interface
* internal/era/e2store: export HeaderSize
* internal/era: refactor era to use ReadAt interface
* internal/era: elevate anonymous func to named
* cmd/utils: don't store entire era file in-memory during import / export
* internal/era: better abstraction between era and e2store
* cmd/era: properly close era files
* cmd/era: don't let defers stack
* cmd/geth: add description for import-history
* cmd/utils: better bytes buffer
* internal/era: error if accumulator has more records than max allowed
* internal/era: better doc comment
* internal/era/e2store: rm superfluous reader, rm superfluous testcases, add fuzzer
* internal/era: avoid some repetition
* internal/era: simplify clauses
* internal/era: unexport things
* internal/era,cmd/utils,cmd/era: change to iterator interface for reading era entries
* cmd/utils: better defer handling in history test
* internal/era,cmd: add number method to era iterator to get the current block number
* internal/era/e2store: avoid double allocation during write
* internal/era,cmd/utils: fix lint issues
* internal/era: add ReaderAt func so entry value can be read lazily
Co-authored-by: lightclient <lightclient@protonmail.com>
Co-authored-by: Martin Holst Swende <martin@swende.se>
* internal/era: improve iterator interface
* internal/era: fix rlp decode of header and correctly read total difficulty
* cmd/era: fix rebase errors
* cmd/era: clearer comments
* cmd,internal: fix comment typos
---------
Co-authored-by: Martin Holst Swende <martin@swende.se>
