[rust] Fixes memory leak

[frankfliu]

Fixes: #3413

Description

Brief description of what this PR is about

• If this change is a backward incompatible change, why must this change be made?
• Interesting edge cases to note here

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 58.38%. Comparing base (cb898a6) to head (ffbbc4e).
Report is 10 commits behind head on master.

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Additional details and impacted files

@@              Coverage Diff              @@
##             master    #3433       +/-   ##
=============================================
- Coverage     72.53%   58.38%   -14.15%     
+ Complexity     7372     5786     -1586     
=============================================
  Files           668      669        +1     
  Lines         32629    32658       +29     
  Branches       3468     3474        +6     
=============================================
- Hits          23667    19068     -4599     
- Misses         7347    12116     +4769     
+ Partials       1615     1474      -141     

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