Add test for Base.unsafe_indices(::SymRange) to reach 100% coverage

[kdw503]

Summary

• Adds a direct test for Base.unsafe_indices(::SymRange), the one line missing from coverage
• Brings test coverage from 98.4% → 100%

Test plan

• Pkg.test() passes (20/20 SymRange tests, 140 total)
• Coverage confirmed at 100% via CoverageTools.jl

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (6843f29) to head (b8ddcd9).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master       #24      +/-   ##
===========================================
+ Coverage   98.61%   100.00%   +1.38%     
===========================================
  Files           2         2              
  Lines          72        72              
===========================================
+ Hits           71        72       +1     
+ Misses          1         0       -1     

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