test(bitcoind): lock JSON-RPC 2.0 success handling (no error key)

Bitcoin Core 28+ replies to a JSON-RPC 2.0 request with a strict 2.0
response: a success has a 'result' key but no 'error' key. The v1.11 code
did 'if result["error"] is not None' and crashed with KeyError: 'error'.
The getters are already guarded on dev with 'if "error" in result and
...'; add regression tests for get_network_info / get_blockchain_info so
that guard can't be dropped again (verified they fail against the old
unguarded form).

Fixes #277

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/test_bitcoin_rpc_success.py

@@ -0,0 +1,41 @@
+"""
+Regression test for blitz_api#277.
+
+Bitcoin Core 28+ answers a JSON-RPC 2.0 request with a strict 2.0 response:
+a successful reply contains a "result" key but no "error" key. The old code
+did `if result["error"] is not None` and crashed with KeyError: 'error'.
+get_network_info / get_blockchain_info must handle a success response that
+has no "error" key.
+"""
+
+from app.bitcoind import service
+
+
+async def test_get_network_info_success_without_error_key(monkeypatch):
+    # strict JSON-RPC 2.0 success payload: note there is NO "error" key
+    async def fake_rpc(method, params=[]):
+        return {"jsonrpc": "2.0", "result": {"stub": "networkinfo"}, "id": 1}
+
+    monkeypatch.setattr(service, "bitcoin_rpc_async", fake_rpc)
+    monkeypatch.setattr(
+        service.NetworkInfo, "from_rpc", staticmethod(lambda result: result)
+    )
+
+    # must not raise / swallow-to-None on the missing "error" key
+    out = await service.get_network_info()
+
+    assert out == {"stub": "networkinfo"}
+
+
+async def test_get_blockchain_info_success_without_error_key(monkeypatch):
+    async def fake_rpc(method, params=[]):
+        return {"jsonrpc": "2.0", "result": {"stub": "blockchaininfo"}, "id": 1}
+
+    monkeypatch.setattr(service, "bitcoin_rpc_async", fake_rpc)
+    monkeypatch.setattr(
+        service.BlockchainInfo, "from_rpc", staticmethod(lambda result: result)
+    )
+
+    out = await service.get_blockchain_info()
+
+    assert out == {"stub": "blockchaininfo"}