Fix atuin daemon on darwin

[utkarshgupta137]

Description

With atuin 18.4.0, it looks for the socket file in XDG_RUNTIME_DIR by default. But the launchd daemon we run doesn't have access to that variable, so it is created at the default socket_path which is XDG_DATA_HOME/atuin.
To fix this, we provide a default value for the socket path which is XDG_DATA_HOME/atuin/daemon.sock

Checklist

• Change is backwards compatible.

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Maintainer CC

@hawkw @water-sucks

[rycee]

Thanks for the contribution. Added a few comments.

[water-sucks]

@rycee In my original PR, I went with letting atuin configure the daemon socket path itself at .local/share/atuin/atuin.sock due to this very issue of launchd not seeing XDG variables.

AFAIK it used to fall back to this path if XDG_RUNTIME_DIR is not found, but @utkarshgupta137 is right about atuin using XDG_RUNTIME_DIR only though from 18.4.0 onward (https://github.com/atuinsh/atuin/blob/05aec6f8d60409af0f58942e1550e1a6a3b3b0ce/crates/atuin-client/src/settings.rs#L730), which is quite the change, but I digress.