This PR completes the implementation of `eth_getProof` by adding support
for storage proofs.
Because storage proofs are potentially overlapping, the existing
strategy of simply aggregating all proofs together into a single result
was challenging. Instead, this commit rewires things to introduce a
ProofRetainer, which aggregates proofs and their corresponding nibble
encoded paths in the trie. Once all of the proofs have been aggregated,
the caller requests the proof result, which then iterates over the
aggregated proofs, placing each into the relevant proof array into the
result.
Although there are tests for `eth_getProof` as an RPC and for the new
`ProofRetainer` code, the code coverage for the proof generation over
complex tries is lacking. But, since this is not a new problem I'll plan
to follow up this PR with an additional one adding more coverage into
`turbo/trie`.
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Co-authored-by: Jason Yellick <jason@enya.ai>
