Added support for nextDate and enumerateDates to Calendar

[fhasse95]

This PR extends the Calendar class to include support for nextDate and enumerateDates.

The core logic was primarily adapted from the Swift Foundation repository repository to ensure parity with the native Swift behavior and minimize the risk of logic errors inherent in a full reimplementation. Since Skip currently only supports the Gregorian calendar, non-essential special cases were removed (e.g., lunar calendar offsets).

To ensure stability, I added several unit tests covering ranges, intervals, and enumeration. However, due to the complexity of calendar edge cases, it's possible that I overlooked a scenario.

Therefore, if you notice anaything, please let me know! 😊

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• AI was used to generate or assist with generating this PR. Please specify below how you used AI to help you, and what steps you have taken to manually verify the changes.

I used AI for assistance in creating additional unit tests for the calendar components and for consulting on Java-specific Calendar behaviors. Verification was done by manually reviewing all test cases, adjusting range expectations to match platform-specific constants, and ensuring the tests pass on both environments.

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[marcprux]

This STOP_EXHAUSTIVE_SEARCH_AFTER_MAX_ITERATIONS approach seems rather heavy-handed to me. I assume there's no equivalent function in Java's Calendar logic?

How does Foundation's Calendar do it?

[fhasse95]

As far as I know, Java's Calendar does not have a direct native equivalent to Apple's enumerateDates function which is why I decided to base the implementation on the logic found in the Swift Foundation library.

I agree that this approach seems heavy-handed for preventing infinite loops. However, the Swift Foundation implements it in exactly the same way (see: https://github.com/swiftlang/swift-foundation/blob/main/Sources/FoundationEssentials/Calendar/Calendar_Enumerate.swift#L472C9-L472C62).