Expand the legacy getLyrics e2e coverage from a single embedded-plain case to a
table over all six fixtures: embedded LRC/plain/TTML and sidecar LRC/SRT/YAML.
Each case asserts the v1 plain-text fallback contract — the structured lyric is
flattened to LRC-style plain text with no timing markup leaking through (no LRC
brackets, SRT arrows, or XML tags), regardless of the source format or whether
it is embedded or a sidecar file. This pins the behavior that synced TTML/SRT/
YAML formats degrade gracefully to plain text on the legacy endpoint.