feature: Add packed user op for EntryPoint v0.7

[veljkovranic]

📖 Context

Type of change

• Non-breaking change (backwards compatible)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Why are we doing this

Entypoint v0.7 smart contract introduces a new PackedUserOperation type that packs the following fields

• accountGasLimits as (concatenation of verificationGas (16 bytes) and callGas (16 bytes))
• gasFees (concatenation of maxPriorityFee (16 bytes) and maxFeePerGas (16 bytes))

To achieve this, we introduce packAccountGasLimits and packGasFees, both relying on packUint methods.

To be able to undo the packing operation, this PR introduces unpacking methods for PackedUserOperation, with the necessary helper functions.

Related issues:

• Implement the PackedUserOperation #669

What did we do?

• Implemented packing/unpacking + encoding/hashing methods for new UserObject in EntryPoint v0.7

How Has This Been Tested?

• Added unit tests that check simple cases + real-world example from transaction of Base Sepolia (link provided in the comment)

[TheDivic]

Good job on the implementation! 🥇

Please just add some comments and docs.