Changing a column's Value Aggregation only persisted if another piece of grid
state (such as a sort) changed at the same time, because the grid-state change
detector hashed only column order, sorts and filters. This matches the
reported workaround (trigger a sort, then Update chart).
Include per-column aggFunc in the capture signature so the change is detected
and saved on its own. Same root cause as #107166.
Add unit tests for the Explore 'change aggregation then Update chart' scenario.
