[codex] Fix ordinal-only export parsing

[dguido]

Summary

• parse export directories when VirtualAddress is present even if Size is zero
• include ordinal-only exports while skipping empty EAT slots
• preserve named export ordering and avoid partial export insertion on malformed zero-size directories
• add synthetic export fixture coverage plus a real Corkami dllemptyexp.dll regression test

Validation

• ctest --test-dir passed in Debug/Release and shared/static builds
• Debug shared/static ASan+UBSan builds passed full CTest (15/15 each)
• direct IterExpFull differential over Corkami: 231 scanned, 184 comparable, 24 exports matched, 0 mismatches
• sanitizer dump-pe smokes passed for tests/assets/example.exe and Corkami dllemptyexp.dll
• pepy wheel and sdist build/install/smoke passed
• git diff --check
• full tracked-source clang-format --dry-run -Werror -style=file