Fixes#31916. Snapshot the on-disk size of the prunable chain-freezer
tables (bodies and receipts) before and after the prune step, and
include the delta as cleared= on the existing "History pruning
completed" log line. Operators see the impact of the run immediately
without inspecting the data directory by hand.
The header and hash tables are intentionally excluded from the
measurement because they are configured with prunable=false and are
never truncated. If AncientSize fails for any table the helper
returns 0 so the log shows "cleared=0.00 B" rather than a partial,
misleading figure.
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