Add keyset cursor pagination to `$find`

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What this task asks for

Add cursor-based keyset pagination to `$find` with nextCursor handling and validation. Add keyset pagination through a `cursor` option on `$find`. Return `nextCursor` for ordered limited queries only when more results remain. Encode sort values, the configured entity ID, and normalized sort directions in a Base64 JSON cursor. Support single- and multi-column ordering in ascending or descending directions. Return HTTP 400 for incompatible offset use, missing ordering, malformed cursors, mismatched sorting, or a missing entity ID.