chore: Update core extension to 0.5.2

[Chriztiaan]

This updates the core extension used by the SDK to 0.5.2, to help make the update easier I used the following sibling SDK update PRs as reference:

1. Time values are now encoded as microsecond timestamps (instead of seconds).
2. The $local bucket is gone, we need to use the new powersync_control('target_checkpoint_request_id') interface to store a checkpoint request after uploading crud data.
3. We need to call most core extension functions in transactions, they no longer start one automatically.

• Kotlin 5.1
• Kotlin 5.2
• Dart 5.1
• Dart 5.2
• JS 5.1/5.2

AI Disclosure

I used Claude Opus 5 to help investigate, design, and implement this solution.

[simolus3]

Just one drive-by comment from my side, the rest of this looks like a good port of relevant changes.

[LucDeCaf]

Looks good. This will be helpful for implementing checkpoint requests in the future.