Remote ordered-position count traffic

Remote AdsGetRelKeyPos now asks for a physical record count only in natural order. With an active index, it uses the existing scoped key count and skips the physical value that it would otherwise discard.

The nested remote position jump uses the same rule. AdsSetRelKeyPos keeps its existing physical-count target calculation and passes that snapshot to the natural-order jump instead of asking the helper to ensure it again. Under the current cached-count policy, that second ensure normally already costs no RPC. This port does not promise an additional wire reduction for that setter today. An ordered jump still uses the scoped key count to clamp its target.

Pending buffered writes are still flushed before a jump. Index activation, scope handling, count/key caches, natural-order movement and error checks keep their existing behavior. No protocol, Harbour RDD core, record-lock contract, count freshness policy or OPENADS_FRESH_COUNTS option is changed.

Tests explicitly clear only the physical-count cache to measure the discarded RPC. They check table and index handles, a narrower numeric scope, preserved setter targets and natural-order get/set behavior. Clearing this cache in the test is not a production freshness option.