Updates the assertion in test_resolve_level2_unmapped_code to use the new
diagnostic message format designed in bf-w1o10.
- Changed bare assert!(result.is_failure()) to assert!(result.is_failure(), "...")
- Added structured message with Expected/Found/Why this matters sections
- Clarifies that codes above 0x7F in StandardEncoding are unmapped per build/unmapped-glyph-names.json
This completes the assertion message update task. All other unmapped glyph
assertions in unmapped.rs, encoding.rs, and test files were already updated
with the new format.
Closes bf-5dopl. All unmapped glyph tests pass (unmapped, encoding, resolver, cmap).
9c0f18c117