Remove ethereum-serai/serai-processor-ethereum-contracts

contracts was smashed out of ethereum-serai. Both have now been smashed into
individual crates.

Creates a TODO directory with left-over test code yet to be moved.

processor/ethereum/TODO/contracts/tests/ERC20.sol

@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: AGPL-3.0-only
+pragma solidity ^0.8.26;
+
+contract TestERC20 {
+  event Transfer(address indexed from, address indexed to, uint256 value);
+  event Approval(address indexed owner, address indexed spender, uint256 value);
+
+  function name() public pure returns (string memory) {
+    return "Test ERC20";
+  }
+
+  function symbol() public pure returns (string memory) {
+    return "TEST";
+  }
+
+  function decimals() public pure returns (uint8) {
+    return 18;
+  }
+
+  function totalSupply() public pure returns (uint256) {
+    return 1_000_000 * 10e18;
+  }
+
+  mapping(address => uint256) balances;
+  mapping(address => mapping(address => uint256)) allowances;
+
+  constructor() {
+    balances[msg.sender] = totalSupply();
+  }
+
+  function balanceOf(address owner) public view returns (uint256) {
+    return balances[owner];
+  }
+
+  function transfer(address to, uint256 value) public returns (bool) {
+    balances[msg.sender] -= value;
+    balances[to] += value;
+    return true;
+  }
+
+  function transferFrom(address from, address to, uint256 value) public returns (bool) {
+    allowances[from][msg.sender] -= value;
+    balances[from] -= value;
+    balances[to] += value;
+    return true;
+  }
+
+  function approve(address spender, uint256 value) public returns (bool) {
+    allowances[msg.sender][spender] = value;
+    return true;
+  }
+
+  function allowance(address owner, address spender) public view returns (uint256) {
+    return allowances[owner][spender];
+  }
+}