fix(tts): don't let a self-closing prosody marker swallow the next expr tag

[chuenchen309]

What

_EXPR_WRAP_RE (the regex that matches a wrapping <expr type="prosody"|"spell">...</expr> marker) matched any <expr ...type="prosody"|"spell"...> up to its first > — which also matches the closing /> of a self-closing point control like <expr type="prosody" label="slow"/>. When a self-closing prosody marker appears before a later wrapping marker (e.g. a spell tag), the lazy inner group swallows everything up to the next </expr>, merging the two markers and dropping the second marker's own conversion.

Repro (before fix):

text = 'Say it slow: <expr type="prosody" label="slow"/> and now spell it: <expr type="spell">A7X9</expr> done.'
convert_markup("cartesia", text)
# 'Say it slow: <speed ratio="0.85"/> and now spell it: A7X9 done.'
#                                                        ^^^^ spell wrapping lost — should be <spell>A7X9</spell>

Fix

Added a negative lookbehind ((?<!/)) before the opening tag's closing > so _EXPR_WRAP_RE never matches a self-closing tag as a wrap opener — those are left for _EXPR_SELF_RE to handle on its own pass, as intended.

Testing

• New regression test test_convert_expr_cartesia_self_closing_prosody_before_spell — red before the fix (asserted, see commit), green after.
• Full tests/test_expr_markup.py (42 tests) and tests/test_tokenizer_xml_markup.py (38 tests) pass.
• ruff check / ruff format --check clean on both changed files.

AI disclosure

Investigated and implemented with Claude Code (Claude Opus 4.8); I reviewed the diff, ran the repro and full test suite myself before opening this PR.

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.