GeezerVison

SolveSpaceUI::Clear() leaves the linked-sketch caches populated. Their cached Sketch objects are owned through raw pointers and need the explicit cleanup already provided by ClearLinkedSketches(). If a linked-file test runs last, shutdown leaks those objects and their allocations. Starting another sketch clears the caches, which makes the failure depend on the shuffled test order.

Call ClearLinkedSketches() during UI cleanup, covering application/CLI shutdown and test teardown.

This addresses the Ubuntu sanitizer failure reported in #1813. group/link/normal_roundtrip alone reproduces the same 45,428-byte leak in 17 allocations on master abf33ac. It also reproduces with the two helix files restored to their pre-#1813 versions from b34d744, so the leak predates that PR.

Tested in a Debug headless build with GCC 11.4, ENABLE_SANITIZERS=ON, ENABLE_OPENMP=ON, leak detection enabled and three OpenMP threads. The isolated reproducer and all 300 tests (1,246 checks) pass without sanitizer errors after the fix. The full suite used seed 2062209549 from the failing CI run; before the fix it reproduces the same leak. No interactive GUI testing was performed.