merger: 使用 sqlx.Scanner 来读取数据

[flycash]

为进一步解决事务，提前替换了

[codecov[bot]]

Codecov Report

Merging #216 (8b29821) into dev (d918cee) will decrease coverage by 2.37%. Report is 1 commits behind head on dev. The diff coverage is 61.58%.

@@            Coverage Diff             @@
##              dev     #216      +/-   ##
==========================================
- Coverage   85.65%   83.29%   -2.37%     
==========================================
  Files          48       50       +2     
  Lines        3653     3873     +220     
==========================================
+ Hits         3129     3226      +97     
- Misses        415      530     +115     
- Partials      109      117       +8     

Files Changed	Coverage Δ
internal/merger/batchmerger/merger.go	88.33% <20.00%> (-6.22%)	:arrow_down:
internal/datasource/single/db.go	55.00% <28.57%> (-16.43%)	:arrow_down:
sharding_select.go	60.58% <38.46%> (-13.06%)	:arrow_down:
...l/datasource/shardingsource/sharding_datasource.go	56.52% <40.74%> (-20.41%)	:arrow_down:
internal/datasource/cluster/cluster_db.go	60.00% <45.45%> (-21.82%)	:arrow_down:
...nternal/merger/groupby_merger/aggregator_merger.go	82.03% <57.14%> (-1.58%)	:arrow_down:
internal/merger/aggregatemerger/merger.go	93.02% <70.00%> (-0.51%)	:arrow_down:
...ernal/datasource/transaction/single_transaction.go	73.33% <73.33%> (ø)
...ternal/datasource/transaction/delay_transaction.go	90.32% <90.32%> (ø)
internal/datasource/transaction/types.go	91.66% <91.66%> (ø)
... and 1 more

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