Rewrite `test_bitcoin_failure` to reflect synchronous bcli behavior: the node now crashes on invalid bitcoind responses rather than retrying. Add `may_fail` and `broken_log` to handle expected crash.
Update `test_bitcoind_fail_first` stderr check to match the new error message format from `get_bitcoin_result`.
Update test mocks to use proper error format for "block not found".
Co-authored-by: ShahanaFarooqui <shahana.farooqui@gmail.com>