Rename the coins folder to networks (#583)

* Rename the coins folder to networks

Ethereum isn't a coin. It's a network.

Resolves #357.

* More renames of coins -> networks in orchestration

* Correct paths in tests/

* cargo fmt

networks/ethereum/contracts/Sandbox.sol

@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: AGPLv3
+pragma solidity ^0.8.24;
+
+struct Call {
+  address to;
+  uint256 value;
+  bytes data;
+}
+
+// A minimal sandbox focused on gas efficiency.
+//
+// The first call is executed if any of the calls fail, making it a fallback.
+// All other calls are executed sequentially.
+contract Sandbox {
+  error AlreadyCalled();
+  error CallsFailed();
+
+  function sandbox(Call[] calldata calls) external payable {
+    // Prevent re-entrancy due to this executing arbitrary calls from anyone
+    // and anywhere
+    bool called;
+    assembly { called := tload(0) }
+    if (called) {
+      revert AlreadyCalled();
+    }
+    assembly { tstore(0, 1) }
+
+    // Execute the calls, starting from 1
+    for (uint256 i = 1; i < calls.length; i++) {
+      (bool success, ) =
+        calls[i].to.call{ value: calls[i].value }(calls[i].data);
+
+      // If this call failed, execute the fallback (call 0)
+      if (!success) {
+        (success, ) =
+          calls[0].to.call{ value: address(this).balance }(calls[0].data);
+        // If this call also failed, revert entirely
+        if (!success) {
+          revert CallsFailed();
+        }
+        return;
+      }
+    }
+
+    // We don't clear the re-entrancy guard as this contract should never be
+    // called again, so there's no reason to spend the effort
+  }
+}