Avoid repeated copying while assembling long Tool history turns #1012

Loading an older folded Tool turn can require up to 250 backend pages. The
current loadDirectHistoryTurn prepends every page by copying the entire
previous result, so assembling N rows across P pages takes O(N * P) reference
copies. A 5,000-row / 250-page turn copies 627,500 row references before it can
be displayed.

Keep the fetched pages until the turn boundary is known and flatten them once
in chronological order. Preserve the existing cursor, request-budget, and
all-or-error publication contracts.