Improve borm mutation output completeness

[lveillard]

Enhance SurrealDB mutation outputs to provide complete deltas, impacted IDs, and deleted/unlinked values.

Previously, BORM's SurrealDB mutation outputs lacked complete information, especially for unlink operations, event-driven changes, and full data for deleted items. This PR ensures all create, update, and delete operations, including those on edges and reference fields, generate comprehensive delta records with before and after states. It also makes deleted/unlinked data visible by using the before state when after is absent, providing full impacted IDs and supporting $fields for deletions.

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[cursor]

Cursor Agent can help with this pull request. Just @cursor in comments and I'll start working on changes in this branch.
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