fix(erc7562): enable state diffs to capture SLOAD in accessedSlots.reads

[stephancill]

The erc7562Tracer config starts from Self::none() which sets record_state_diff: false. This causes SLOAD operations to not populate accessedSlots.reads because the SLOAD handler in geth_erc7562_traces() depends on step.storage_change, which is only set when record_state_diff is enabled.

Problem

// geth_erc7562_traces() — SLOAD handler (builder/geth.rs:427)
opcode::SLOAD => {
    if let Some(stack) = &step.stack {
        if let Some(slot) = stack.get(stack.len().saturating_sub(1)) {
            if !already_read && !already_written {
                if let Some(change) = &step.storage_change {  // <-- always None
                    accessed_slots.reads.entry(slot).or_default().push(value);
                }
            }
        }
    }
}

step.storage_change is only populated in step_end() when self.config.record_state_diff is true:

// tracing/mod.rs:554
step.storage_change = if matches!(op, opcode::SLOAD | opcode::SSTORE) {
    // only reached when record_state_diff is true

But from_geth_erc7562_config() never enables it:

pub fn from_geth_erc7562_config(config: &Erc7562Config) -> Self {
    Self::none()                         // record_state_diff: false
        .set_record_logs(...)
        .set_memory_snapshots(true)
        .set_stack_snapshots(StackSnapshotType::Full)
        .steps()                         // missing .set_state_diffs(true)
}

Steps to reproduce

1. Start a reth node and deploy a contract that uses SLOAD (e.g. a counter with get() and increment()):

contract Counter {
    uint256 public count;
    function increment() external { count += 1; }
}

2. Call increment() a few times so slot 0 has a non-zero value.

3. Trace an increment() call with the erc7562Tracer:

curl -X POST http://localhost:8545 -H "Content-Type: application/json" -d '{ 
  "jsonrpc": "2.0", "id": 1,
  "method": "debug_traceCall",
  "params": [{
    "to": "<counter_address>",
    "data": "0xd09de08a"
  }, "latest", {"tracer": "erc7562Tracer"}]
}'

4. Observe that accessedSlots.reads is empty even though increment() does SLOAD on slot 0 before SSTORE:

{
  "accessedSlots": {
    "reads": {},
    "writes": {"0x00..00": 1}
  }
}

Expected: reads should contain {"0x00..00": ["<current_value>"]} because the EVM performs an SLOAD before the SSTORE in count += 1.

Actual: reads is always empty.

Note: geth's implementation of the same tracer correctly populates accessedSlots.reads.

Impact

ERC-4337 bundlers (e.g. Rundler) need (slot, initial_value) pairs from SLOAD to enforce ERC-7562 storage access rules ([STO-010], [STO-031], etc.). Without this fix, the native erc7562Tracer cannot replace custom JS tracers, which are 4-100x slower due to per-opcode JS interpretation.

Fix

One line: .set_state_diffs(true) in from_geth_erc7562_config().