optimize(api): make condition task precede more user-friendly

[Tangxinqi]

Optimize ConditionTask.Precede by replacing i with len(cond.mapper) to resolve abnormal flow execution results caused by multiple calls to precede

[Tangxinqi]

ap

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.52%. Comparing base (f8e1652) to head (5ec09af).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #103      +/-   ##
==========================================
+ Coverage   88.50%   88.52%   +0.01%     
==========================================
  Files          13       13              
  Lines         783      784       +1     
==========================================
+ Hits          693      694       +1     
  Misses         71       71              
  Partials       19       19              

Flag	Coverage Δ
unittests	88.52% <100.00%> (+0.01%)	⬆️

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[noneback]

LGTM