feat(adk): add ut for agent tool copy stream

[meguminnnnnnnnn]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.47%. Comparing base (5732c76) to head (62f2a2d).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #668      +/-   ##
==========================================
+ Coverage   80.34%   80.47%   +0.12%     
==========================================
  Files         124      124              
  Lines       11906    11906              
==========================================
+ Hits         9566     9581      +15     
+ Misses       1608     1595      -13     
+ Partials      732      730       -2     

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