Fix sizeof in test allocator mock

[PJK]

Summary

• Fix sizeof(expectations) (pointer size) to sizeof(*expectations) (element size) in test/test_allocator.c
• In practice this over-allocates on 64-bit (pointer > enum) so no runtime issue, but the intent is wrong

Test plan

• All 26 tests pass (this is the foundation of all allocation-failure tests)

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (17d9433) to head (bc01665).
⚠️ Report is 27 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #396   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           20        20           
  Lines         1663      1663           
=========================================
  Hits          1663      1663           

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