fix: treat address-only getsourcecode responses as unverified contracts

[jsvisa]

Some Blockscout-compatible explorers return an address-only payload for contract/getsourcecode on non-contract
addresses, e.g.:

request on https://zetascan.com/api?module=contract&action=getsourcecode&address=0xBB9bc244D798123fDe783fCc1C72d3Bb8C189413 returns:

{ "message": "OK", "result": [{ "Address": "0x..." }], "status": "1" }

foundry-block-explorers currently tries to deserialize this into ContractMetadata, which fails and emits noisy
Failed to deserialize response logs:

2026-03-03T03:40:27.827090Z ERROR etherscan: Failed to deserialize response: data did not match any variant of untagged enum ResponseData res="{\"message\":\"OK\",\"result\":[{\"Address\":\"0x7109709ecfa91a80626ff3989d68f67f5b1dd12d\"}],\"status\":\"1\"}"
2026-03-03T03:40:27.830366Z ERROR etherscan: Failed to deserialize response: data did not match any variant of untagged enum ResponseData res="{\"message\":\"OK\",\"result\":[{\"Address\":\"0xe98448ee92eb6cd06366febd70f7f11307fd9a2c\"}],\"status\":\"1\"}"
2026-03-03T03:40:27.831478Z ERROR etherscan: Failed to deserialize response: data did not match any variant of untagged enum ResponseData res="{\"message\":\"OK\",\"result\":[{\"Address\":\"0x000000000000000000636f6e736f6c652e6c6f67\"}],\"status\":\"1\"}"
2026-03-03T03:40:27.845193Z ERROR etherscan: Failed to deserialize response: data did not match any variant of untagged enum ResponseData res="{\"message\":\"OK\",\"result\":[{\"Address\":\"0x0000000000000000000000000000000000000000\"}],\"status\":\"1\"}"

[mattsse]

this makes sense, ty!