Optimize `output_script` getter to avoid cloning in `InvalidIdentityCreditWithdrawalTransitionOutputScriptError`

[coderabbitai]

As identified in PR #2191 comment by @shumkov, the output_script getter currently clones the CoreScript, which may introduce unnecessary overhead. This issue is to track the optimization of the output_script getter to avoid cloning for improved performance.

[thepastaclaw]

Closing — the InvalidIdentityCreditWithdrawalTransitionOutputScriptError type no longer exists in the codebase. The code this optimization targeted has been removed.