Add ABI v2 cached reference support

[andimarafioti]

Summary

Updates the Python bindings for qwentts.cpp ABI v2 and pins wheel builds to upstream 4536dcdce27c3764a93a06d6bf64026b124962f5.

What changed

• Added ABI v2 tail fields to qt_tts_params: ref_spk_emb, ref_spk_dim, ref_codes, ref_T.
• Added optional binding for qt_num_codebooks, qt_n_speakers, and qt_speaker_name.
• Added QwenTTS.num_codebooks(), QwenTTS.speaker_names(), and QwenTTS.load_rvq_codes().
• Added load_speaker_embedding() and load_rvq_codes() helpers for .spk / .rvq files from qwen-codec --talker.
• Added ref_spk_emb and ref_codes to buffered and streaming synthesis calls.
• Bumped the package version to 0.1.0a1.

Validation

• uv run --with pytest --with numpy --with huggingface-hub pytest -q -> 5 passed, 1 skipped
• Built a CPU libqwen from qwentts.cpp 4536dcdce27c3764a93a06d6bf64026b124962f5.
• Loaded a real 1.7B Base Q4 model with the new library and verified:
  • QwenLibrary().version() returns 4536dcd (2026-06-21)
  • ABI v2 helper symbols are present
  • .spk loads as a 2048-dim float32 vector
  • .rvq loads as a [16, 215] int32 matrix
  • synthesis succeeds with ref_spk_emb
  • synthesis succeeds with ref_spk_emb + ref_codes + ref_text
• uv run --with build python -m build --wheel --outdir /tmp/qwentts-cpp-python-abi-v2-dist
• Imported the built 0.1.0a1 wheel and loaded its bundled library successfully.