💥 `ERC-4337` Functionalities

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I consider the following ERC-4337 functionalities important to have for 🐍 snekmate:

• SimpleAccount (example); additionally to the common secp256k1-based elliptic curve verification, we should also offer a variant with the secp256r1-based elliptic curve verification. I have written a Vyper-based verifier here; also see #175;
• SimpleAccountFactory (example);
• BLSAccount (example); minimal BLS-based account that uses an aggregated signature;
• BLSAccountFactory (example);
• TokenPaymaster (example); a sample ERC-20 token paymaster for ERC-4337;

References

• https://github.com/eth-infinitism/account-abstraction
• https://github.com/de33/vyper-erc4337