fix: harden ordinal realization and equivalence

[aryamantodkar]

Summary

• accept optional articles, conjunctions, hyphenated ordinal words, and ordinal scales through undecillionth
• support canonical numeric suffix and Roman numeral forms
• reject invalid suffixes, signs, malformed Roman forms, and unrelated trailing text
• add evaluation-only ordinal equivalence without adding display aliases to runtime candidates
• document ordinal coverage and add regression tests

Validation

• cargo test --manifest-path rust/Cargo.toml
• uv run pytest
• uv run ruff check .

This PR is stacked on #42.