Add async methods to source contracts clients

[moisses89]

Description

• Add asynchronous methods of SourcifyClient, EtherscanClientV2 and BlockScoutClient.
• EtherscanClient V1 is not included.

Considerations

It was necessary extend the class with different method names because mypy does not let override functions with async and not asynchronous applications could have troubles generating aiohttp session.

[coveralls]

Pull Request Test Coverage Report for Build 12582597053

Details

• 159 of 175 (90.86%) changed or added relevant lines in 7 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.05%) to 93.887%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
safe_eth/eth/clients/sourcify_client.py	25	26	96.15%
safe_eth/eth/clients/etherscan_client.py	19	21	90.48%
safe_eth/eth/tests/clients/test_sourcify_client.py	24	26	92.31%
safe_eth/eth/clients/blockscout_client.py	25	28	89.29%
safe_eth/eth/tests/clients/test_etherscan_client_v2.py	21	24	87.5%
safe_eth/eth/clients/etherscan_client_v2.py	33	38	86.84%

Files with Coverage Reduction	New Missed Lines	%
safe_eth/eth/clients/sourcify_client.py	1	90.48%

Totals
Change from base Build 12544314072:	-0.05%
Covered Lines:	9430
Relevant Lines:	10044

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💛 - Coveralls