[Fix] Force GC after final batch to release all Redis connections

[Fix] Force GC after final batch to release all Redis connections

Previously GC was skipped for the final batch (batch_end >= #results),
leaving those connections checked out. The subsequent DEL of idx_key
could hit the pool limit if batch_size was near the limit, leaving the
_processing key behind and exhausting the pool for the next date.

Now collectgarbage() runs after every batch including the last one,
ensuring all connections are released before the DEL operation.