[Instrumentation.WCF] AspNetParentSpanCorrector fixes

[Kielek]

Follow up to #3151

Changes

While reviewing consider checking each commit independently. Fixes 3 issues, the one related to recursion is critical.

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• [ ] Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.09%. Comparing base (8b5340d) to head (48b815f).
⚠️ Report is 3 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3248   +/-   ##
=======================================
  Coverage   70.09%   70.09%           
=======================================
  Files         430      430           
  Lines       16941    16946    +5     
=======================================
+ Hits        11874    11879    +5     
  Misses       5067     5067           

Flag	Coverage Δ
unittests-Instrumentation.Wcf	79.68% <100.00%> (+0.13%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...on.Wcf/Implementation/AspNetParentSpanCorrector.cs	95.23% <100.00%> (+0.30%)	⬆️

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