fix: correct pre-existing test mocking issues

[b-l-u-e]

This PR fixes two unrelated test issues so the suite runs reliably without false failures.

1. Backend: test_clamps_target_in_rpc_call (RPC service)

problem: The test mocks _rpc_call with a single return_value. estimate_smart_fee() performs several RPC calls internally (estimatesmartfee, getblockchaininfo, getblockcount, getmempoolfeeratediagram, getblockstats). mock.call_args refers to the last call, not the estimatesmartfee call, so the assertion on the clamped target can raise or assert the wrong thing.

Error observed:

self = <test_rpc_service.TestRpcService testMethod=test_clamps_target_in_rpc_call>

    def test_clamps_target_in_rpc_call(self):
        with patch.object(self.rpc, '_rpc_call', return_value={"feerate": 0.0001}) as mock:
            self.rpc.estimate_smart_fee(1, "unset", 2)
>           self.assertEqual(mock.call_args[0][1][0], 2)  # params[0] should be 2
                             ^^^^^^^^^^^^^^^^^^^^^^^
E           IndexError: list index out of range

tests/test_rpc_service.py:88: IndexError
------------------------------------------------- Captured log call --------------------------------------------------
ERROR    rpc_service:rpc_service.py:204 Failed to include health stats: -1
============================================== short test summary info ===============================================
FAILED tests/test_rpc_service.py::TestRpcService::test_clamps_target_in_rpc_call - IndexError: list index out of range

---

2. Frontend: API constructor

problem: BitcoinCoreAPI did not accept a baseUrl argument. Tests pass new BitcoinCoreAPI('http://test-api:5001') so that fetch is mocked against that URL, but the argument was ignored and the client used /api, so assertions on the request URL fail and tests hit the real proxy instead of the mock.

Error observed:

 FAIL  src/services/api.test.ts
  BitcoinCoreAPI
    ✕ should fetch fee estimate (5 ms)
    ✕ should fetch block count with network info (1 ms)
    ✓ should handle fetch errors (2 ms)

  ● BitcoinCoreAPI › should fetch fee estimate

    expect(jest.fn()).toHaveBeenCalledWith(...expected)

    Expected: "http://test-api:5001/fees/2/economical/2", undefined
    Received: "/api/fees/2/economical/2", undefined

    Number of calls: 1

      22 |
      23 |     const result = await api.getFeeEstimate(2, 'economical', 2);
    > 24 |     expect(fetchMock).toHaveBeenCalledWith('http://test-api:5001/fees/2/economical/2', undefined);
         |                       ^
      25 |     expect(result.feerate).toBe(0.0001);
      26 |   });
      27 |

      at Object.<anonymous> (src/services/api.test.ts:24:23)

  ● BitcoinCoreAPI › should fetch block count with network info

    expect(jest.fn()).toHaveBeenCalledWith(...expected)

    Expected: "http://test-api:5001/blockcount", undefined
    Received: "/api/blockcount", undefined

    Number of calls: 1

      33 |
      34 |     const result = await api.getBlockCount();
    > 35 |     expect(fetchMock).toHaveBeenCalledWith('http://test-api:5001/blockcount', undefined);
         |                       ^
      36 |     expect(result.blockcount).toBe(800000);
      37 |     expect(result.chain_display).toBe('MAINNET');
      38 |   });

      at Object.<anonymous> (src/services/api.test.ts:35:23)

Test Suites: 1 failed, 1 total
Tests:       2 failed, 1 passed, 3 total

[ismaelsadeeq]

Thanks for the fix.
I have taken the frontend fix in #15, the backend issue is from the code, it should not have query the mempool diagram
for estimatesmartfee.

This is fixed now.