delete、update 的完善

[Stone-afk]

1、delete，update 将 buffur 放回 buffur 池 2、update 的 Exec 完善

[codecov[bot]]

Codecov Report

Merging #98 (fe74bad) into main (eacfdac) will decrease coverage by 0.13%. The diff coverage is 86.20%.

:exclamation: Current head fe74bad differs from pull request most recent head ea62c3e. Consider uploading reports for the commit ea62c3e to get more accurate results

@@            Coverage Diff             @@
##             main      #98      +/-   ##
==========================================
- Coverage   81.72%   81.59%   -0.14%     
==========================================
  Files          17       17              
  Lines        1100     1092       -8     
==========================================
- Hits          899      891       -8     
  Misses        171      171              
  Partials       30       30              

Impacted Files	Coverage Δ
db.go	68.88% <ø> (-4.70%)	:arrow_down:
update.go	83.33% <85.18%> (+0.42%)	:arrow_up:
delete.go	77.50% <100.00%> (+0.57%)	:arrow_up:
insert.go	92.30% <100.00%> (+0.09%)	:arrow_up:
internal/model/model.go	91.13% <0.00%> (+0.94%)	:arrow_up:

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