tests: Match Core initializer signature

The CLI fake still accepted an obsolete private keyword after the earlier cleanup. Remove it so a production call using that unsupported argument cannot pass the fake and fail only against real Bitcoin Core. Refs #38.

Author: codex

tests/test_cli.py

@@ -106,7 +106,6 @@ def initialize(
         _ask: Callable[[str], str],
         _tell: Callable[[str], None],
         *,
-        private: bool = True,
         account: int = 0,
         timestamp: int | str = "now",
     ) -> str: