fix: memroy leak in zk_client.cc

[wuxiaobai24]

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  Fix memory leak in zk_client.cc.

• What is the current behavior? (You can also link to an open issue here)
  It should resolve Memory leak in zk_client.cc #1659

• What is the new behavior (if this is a feature change)?

[github-actions]

Linux Test Report

       56 files       183 suites   47m 48s ⏱️
  8 218 tests   8 218 ✔️ 0 💤 0 ❌
12 134 runs  12 134 ✔️ 0 💤 0 ❌

Results for commit 67abe13.

♻️ This comment has been updated with latest results.

[github-actions]

SDK Test Report

  72 files    72 suites   5m 48s ⏱️
172 tests 169 ✔️ 3 💤 0 ❌
212 runs  209 ✔️ 3 💤 0 ❌

Results for commit 67abe13.

♻️ This comment has been updated with latest results.

[codecov]

Codecov Report

Merging #1660 (67abe13) into main (7f7607b) will increase coverage by 0.09%.
The diff coverage is 92.35%.

@@             Coverage Diff              @@
##               main    #1660      +/-   ##
============================================
+ Coverage     67.47%   67.57%   +0.09%     
  Complexity      323      323              
============================================
  Files           607      607              
  Lines        115942   116386     +444     
  Branches       1000     1000              
============================================
+ Hits          78232    78646     +414     
- Misses        37503    37533      +30     
  Partials        207      207              

Impacted Files	Coverage Δ
src/storage/disk_table.h	87.03% <ø> (+0.79%)	⬆️
src/storage/disk_table.cc	82.17% <76.39%> (-1.63%)	⬇️
src/storage/mem_table.h	92.30% <100.00%> (+1.00%)	⬆️
src/storage/table_iterator_test.cc	100.00% <100.00%> (ø)
src/zk/zk_client.cc	84.07% <100.00%> (+0.25%)	⬆️
src/replica/log_replicator.cc	79.47% <0.00%> (-0.33%)	⬇️
src/tablet/tablet_impl.cc	44.03% <0.00%> (-0.29%)	⬇️
hybridse/src/vm/schemas_context.cc	88.62% <0.00%> (-0.22%)	⬇️
src/client/ns_client.cc	44.47% <0.00%> (-0.15%)	⬇️
src/storage/mem_table.cc	76.94% <0.00%> (-0.14%)	⬇️
... and 16 more

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[aceforeverd]

thank you！