gh-145846: Fix memory leak in _lsprof clearEntries() context chain (#145847)

clearEntries() only freed the top currentProfilerContext but did not
walk the previous linked list. When clear() is called during active
profiling with nested calls, all contexts except the top one were
leaked. Fix by iterating the entire linked list, matching the existing
freelistProfilerContext cleanup pattern.

Co-authored-by: Victor Stinner <vstinner@python.org>