EIP-1967 support: transparent proxy pattern

[vbaranov]

#3163

Motivation

Blockscout doesn't support retrieving of implementation from storage point defined by EIP-1967

Changelog

• add eth_getStorageAt call support
• get implementation from 0x360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc storage pointer of proxy contract if implementation getter has nonpayable stateMutability.

Checklist for your Pull Request (PR)

• I added an entry to CHANGELOG.md with this PR
• If I added new functionality, I added tests covering it.
• If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.
• I checked whether I should update the docs and did so by submitting a PR to https://github.com/blockscout/docs
• If I added/changed/removed ENV var, I submitted a PR to https://github.com/blockscout/docs to update the list of env vars at https://github.com/blockscout/docs/blob/master/for-developers/information-and-settings/env-variables.md and I updated the version to master in the Version column. Changes will be reflected in this table: https://docs.blockscout.com/for-developers/information-and-settings/env-variables.
• If I add new indices into DB, I checked, that they are not redundant with PGHero or other tools

[coveralls]

Pull Request Test Coverage Report for Build 3a2ffd42-288f-43ae-b875-d1e303c8e340

• 15 of 29 (51.72%) changed or added relevant lines in 5 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.1%) to 74.257%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
apps/block_scout_web/lib/block_scout_web/controllers/smart_contract_controller.ex	3	4	75.0%
apps/explorer/lib/explorer/chain.ex	9	13	69.23%
apps/explorer/lib/explorer/smart_contract/reader.ex	1	5	20.0%
apps/ethereum_jsonrpc/lib/ethereum_jsonrpc/contract.ex	1	6	16.67%

Files with Coverage Reduction	New Missed Lines	%
apps/block_scout_web/lib/block_scout_web/controllers/chain/market_history_chart_controller.ex	2	71.43%

Totals
Change from base Build 9a51de8e-f3ae-459b-ac50-9ce2b62f7c06:	-0.1%
Covered Lines:	5968
Relevant Lines:	8037

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💛 - Coveralls