Make AdditionalRecordId Sendable (StanfordSpezi#41)

# Make AdditionalRecordId Sendable

## ♻️ Current situation & Problem
This PR makes the `AdditionalRecordId` sendable.


## ⚙️ Release Notes 
* `AdditionalRecordId` is now `Sendable` for improved compatibility


## 📚 Documentation
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## ✅ Testing

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## 📝 Code of Conduct & Contributing Guidelines 

By submitting creating this pull request, you agree to follow our [Code
of
Conduct](https://github.com/StanfordSpezi/.github/blob/main/CODE_OF_CONDUCT.md)
and [Contributing
Guidelines](https://github.com/StanfordSpezi/.github/blob/main/CONTRIBUTING.md):
- [x] I agree to follow the [Code of
Conduct](https://github.com/StanfordSpezi/.github/blob/main/CODE_OF_CONDUCT.md)
and [Contributing
Guidelines](https://github.com/StanfordSpezi/.github/blob/main/CONTRIBUTING.md).

Sources/SpeziAccount/Model/AdditionalRecordId.swift

@@ -11,7 +11,7 @@
 ///
 /// The identifier is built by combining a stable ``AccountService`` identifier and the primary accountID (see ``AccountIdKey``).
 /// Using both, additional data records of a user can be uniquely identified across ``AccountService`` implementations.
-public struct AdditionalRecordId: CustomStringConvertible, Hashable, Identifiable {
+public struct AdditionalRecordId: CustomStringConvertible, Hashable, Identifiable, Sendable {
     /// A stable ``AccountService`` identifier. See ``AccountService/id-83c6c``.
     public let accountServiceId: String
     /// The primary user identifier. See ``AccountIdKey``.