core, state: introduce code reader interface

[rjl493456442]

It's an alternative of #30808

This PR introduces a ContractCodeReader interface with functions defined:

// ContractCodeReader defines the interface for accessing contract code.
type ContractCodeReader interface {
	// Code retrieves a particular contract's code.
	//
	// - Returns nil code along with nil error if the requested contract code
	//   doesn't exist
	// - Returns an error only if an unexpected issue occurs
	Code(addr common.Address, codeHash common.Hash) ([]byte, error)

	// CodeSize retrieves a particular contracts code's size.
	//
	// - Returns zero code size along with nil error if the requested contract code
	//   doesn't exist
	// - Returns an error only if an unexpected issue occurs
	CodeSize(addr common.Address, codeHash common.Hash) (int, error)
}

This interface can be implemented in various ways. Although the codebase currently includes only one implementation, additional implementations could be created for different purposes and scenarios, such as a code reader designed for the Verkle tree approach or one that reads code from the witness.

Notably, this interface modifies the function’s semantics. If the contract code is not found, no error will be returned. An error should only be returned in the event of an unexpected issue, primarily for future implementations.

---

Besides, the original Reader interface is extended with ContractCodeReader, it gives us more flexibility to manipulate the reader with additional logics on top, e.g. Hooks.

// Reader defines the interface for accessing accounts, storage slots and contract
// code associated with a specific state.
type Reader interface {
	ContractCodeReader
	StateReader
}

[s1na]

I think this structure looks very nice. Just had a comment about performance of the multireader.

[MariusVanDerWijden]

This might be a stupid suggestion, but what do you think about renaming the interface a little bit like this:

// ContractCodeReader defines the interface for accessing contract code.
type ContractCodeReader interface {
	// Code retrieves a particular contract's code.
	Code(addr common.Address, codeHash common.Hash) ([]byte, error)

	// CodeSize retrieves a particular contracts code's size.
	CodeSize(addr common.Address, codeHash common.Hash) (int, error)
}

Makes the name of the interface a bit longer, but the methods themselves a bit shorter and a user will still understand that this Reader is for contract code

[rjl493456442]

@MariusVanDerWijden applied!

[rjl493456442]

@s1na @MariusVanDerWijden I have updated the implementation, please take another look.

[s1na]

LGTM

[MariusVanDerWijden]

LGTM

[holiman]

Shouldn't you add it to the code/codeSize caches too, before returning?

[rjl493456442]

The codeSizeCache is filled in the r.Code(addr, codeHash) call.

It's a little bit weird, I can change it if you want.

[holiman]

Oh right, yeah never mind!