Preserve trailing backslashes in name round trips

[claell]

Summary

• Stop processing a terminal backslash twice after the name parser reaches end
  of input.
• Escape only last-name-first sections that are followed by a comma.
• Enable the existing strict and non-strict inverse-property cases instead of
  skipping names with odd trailing backslashes.

Fixes #567.

Validation

• Complete name middleware suite under warnings-as-errors: 689 passed.
• Complete upstream suite: 2,578 passed, 10 skipped, with the four existing
  deprecation warnings in tests/test_entrypoint.py. The two removed skips are
  the now-passing strict and non-strict inverse cases.
• git diff --check: passed.
• The project pre-commit executable was not available in the isolated local
  environment; GitHub CI should independently run the configured hooks.

Review note

This change was developed and validated in a concentrated session rather than
exercised over a long period in production. The broad existing name fixture
matrix now passes without the targeted skip, but careful human review of TeX
escaping semantics is requested.

AI assistance

This pull request was prepared with ChatGPT Codex using GPT-5.6 Sol with high
reasoning effort. Codex assisted with analysis, implementation, branch
isolation, and test execution. Automated validation is not a substitute for
maintainer review.