fiskaltrust.Middleware on iOS

### Is your feature request related to a problem? Please describe.
Right now you can run the middleware locally on android, which enables you to sign receipts without an internet connection. For iOS, this is currently not possible. Many of our customers have little to no stable internet connection at their sites, so having offline functionality across both mobile platforms would greatly help.

### Describe the solution you'd like
Since Apple has somewhat relaxed its rules in recent years, might it be possible by now to have the middleware run on iOS aswell, e.g. through an alternative app store?

### Additional context
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Start by reviewing how the middleware currently runs locally on Android and identify the platform-specific entry points involved in offline receipt signing. Then investigate whether an iOS-compatible deployment path is technically and distribution-wise feasible under Apple's rules. Done means a documented, agreed approach for running the middleware offline on iOS, or a clear explanation of why it is not feasible.

Written by the indexing model from the issue text.