Fix CreateSessionKey ApprovedTargets > 0 Crash (#36)

Fixes memory crash when passing string arrays to native library due to
temporary objects being destroyed before async calls by switching to
persistent FAnsiString containers to ensure stable memory addresses
throughout the async operation lifecycle.

Fixes BLD-25

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## Summary by CodeRabbit

* **Refactor**
* Improved the structure of asynchronous operations for better
reliability.
* Enhanced internal handling of session key targets to ensure stability
during wallet operations.

No changes to visible functionality or public interfaces.

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Author: 0xFirekeeper