Three fixes in update_history_times():
1. Wrap DB operations in try-catch — exception no longer skips the
snapshot restore, preventing permanent loss of accumulated counts
2. Treat get_history_times() -1 return (DB failure) as skip, not as
"record exists" → no more silent UPDATE on non-existent rows
3. Only call update_static and advance last_load_time_ on success,
so a failed persist retries on the next cycle instead of waiting
another rw_time_ minutes
Commit e21b2af changed TaskShm map value from DataRecord (flat array)
to TaskRecord (struct wrapping shm_vector_f), but three call sites in
exp_base.cpp didn't drill into the .data_record member — they called
size()/operator[]/push_back() on TaskRecord itself, which has none.
DataRecord used a fixed float[129600000] consuming 5GB disk even when
collecting only a few hundred data points. Replaced with shm_vector_f
that grows on demand via push_back. Removes the need for rm -rf on
process exit — vector destructor frees memory back to the segment.
Also drops now-unnecessary task_data_size member.
