Allow external ownership for Modules

♻️ Current situation & Problem

When loading modules dynamically using loadModule(_:), Spezi always takes ownership of the Module. Spezi keeps a strong reference until unloadModule(_:) is called. This isn't strictly necessary (with some conditions applying). In some cases it is helpful for framework engineers to not pass ownership to Spezi. Namely, one can make use of being notified when objects are de-initialized (e.g., a framework creating a Module and passing ownership to the framework user and relying on the deinit to be notified when the user deallocated the object).

This PR introduces the concept of ModuleOwnership that can be passed to the updated loadModule(_:ownership:) method. external ownership is available to framework developers via the APISupport SPI.
When specifying external ownership does not keep any strong references to the loaded Module. This required making some changes how resources are automatically cleared (e.g., @Dependency, @Provide, @Modifier or @Model modifiers automatically clean up their resources once their are deallocated). Some features like EnvironmentAccessible are not available when using external ownership as they would inherently imply strong ownership.
Other modules that depend on such modules either maintain a weak reference if they declare it as an optional dependency (in this case the dependency is automatically removed once the Module de-initializes) or a strong reference if declared as a required dependency. In such a case, ownership is shared with that module for the lifetime of the module that declares a required dependency to an externally managed module.

⚙️ Release Notes

• Add support for dynamically loading Modules with external ownership.

📚 Documentation

Documentation was updated for changed interfaces.

✅ Testing

Additional unit testing was added to verify functionality of dynamically loaded modules with external ownership.

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