Fix type stability of src/bound.jl

[odow]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.98%. Comparing base (6c2ca24) to head (1aa259c).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #27      +/-   ##
==========================================
- Coverage   96.00%   95.98%   -0.02%     
==========================================
  Files           4        4              
  Lines         400      399       -1     
==========================================
- Hits          384      383       -1     
  Misses         16       16              

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