[vectorized] (olap) optimize BlockReader's performance - #7642

Proposed changes

make _collect_iter as normal object instead of pointer object
replace _init_agg_state to avoid unnecessary condition branch
prefer to use reference instead of object copy
prefer to use emplace_back rather than push_back
pick the evaluation out from loop
ssb test indicate that this change have 5% improvement nearly(41 seconds reduce to 40.5 seconds)
test SQL: select sum(lo_revenue) as revenue from lineorder join dates on lo_orderdate = d_datekey where d_year = 1993 and lo_discount between 1 and 3 and lo_quantity < 25;

Close related #issue (replace it with issue number if it exists).

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