feat!: regenerate SDK on fern-python-sdk@5.14.20 with TTS-only surface

[luke-speechify]

Regenerated on the current Speechify spec with the latest generator (fern-python-sdk@5.14.20). Brings the SDK shape in line with industry conventions (api_key=, flat client.audio.* namespace) and unlocks the async client + raw-response accessor patterns that come free with the 5.x generator line.

Voice-agents methods and types are not exported from this release. The voice-agents API is public over HTTP today, but has never shipped in speechify-api PyPI releases — the SDK is deliberately scoped to the stable TTS surface (audio.*, voices.*). Voice-agents methods will be added in a future release once that surface is locked.

What changed

• Auth kwarg renamed. Speechify(token=...) is now Speechify(api_key=...). The SPEECHIFY_API_KEY environment variable continues to work without change.
• Method namespace flattened. client.tts.audio.speech(...) → client.audio.speech(...); client.tts.voices.list() → client.voices.list(); and so on across all six methods. The tts. intermediate namespace has been removed so SDK paths mirror the underlying URL paths (/v1/audio/..., /v1/voices/...).
• livekit runtime dependency removed. It was only required by voice-agents helpers; TTS doesn't use it.
• Cross-major generator bump (fern-python-sdk@4.x → 5.x). Internal code structure and some private helpers have changed shape. Public method signatures on audio.speech, audio.stream, voices.list / get / create / delete / download_sample are unchanged from their pre-flatten signatures except for the namespace path.

New in this release

• AsyncSpeechify async client with the same method surface as the sync client.
• .with_raw_response accessor on every sub-client for direct access to the underlying HTTP response — e.g. client.audio.with_raw_response.speech(...).
• Better docstrings on audio.speech and audio.stream documenting the JSON-vs-raw-bytes response distinction between the two endpoints, plus the audio/pcm → audio/L16 Content-Type asymmetry on streaming (24 kHz mono LE PCM).

Release

This PR is the regenerated SDK only. Once merged into master, release-please will open a release PR that bumps the version (to 2.0.0) and updates CHANGELOG.md. Merging the release PR triggers the publish workflow to PyPI.

BREAKING CHANGE: Speechify(token=...) is now Speechify(api_key=...). The tts. namespace has been removed — call sites move from client.tts.audio.speech(...) to client.audio.speech(...) and from client.tts.voices.X to client.voices.X. The livekit extra-dependency has been removed; if you were importing it transitively through speechify-api, install it explicitly. Generator-line crossed 4.x → 5.x, so internal/private code paths have moved.