test: implement naive-receiver challenge solution

[devin-ai-integration]

Implement Naive Receiver Challenge Solution

This PR implements the solution for the Naive Receiver challenge by exploiting the flash loan fee mechanism and using the forwarder contract.

Implementation Details

• Use multicall to batch 10 flash loans and drain receiver's funds
• Implement forwarder request signing with proper deployer key
• Successfully withdraw pool funds to recovery address
• Complete solution in 2 transactions (multicall + forwarder.execute)

Test Results

✅ All tests pass:

[PASS] test_assertInitialState() (gas: 57257)
[PASS] test_naiveReceiver() (gas: 394610)

Solution Overview

1. First transaction: Use multicall to batch 10 flash loans with 1 WETH fee each
2. Second transaction: Use forwarder to withdraw pool funds as feeReceiver

Testing

• Solution tested with --isolate flag
• Meets transaction limit requirement (≤2 transactions)
• All funds successfully transferred to recovery address
• Clean implementation with proper error handling

Link to Devin run: https://app.devin.ai/sessions/f17cdf584d4d4296a45d49a3858d2ccf

[devin-ai-integration]

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