chore: sync sdk code with DeepLearning repo

[ccampbell-aai]

Copybara sync from the internal monorepo (master) → master. Bumps the SDK 0.64.26 → 0.64.29.

All changes are in the synchronous transcription (SyncTranscriber) surface.

0.64.27 — language_codes

• Replace the sync language_code option with language_codes (a list) for multi-language synchronous transcription.

0.64.28 — opt-in word timestamps

• Add opt-in word timestamps to SyncTranscriptionConfig. When enabled, sync words carry accurate start/end timings at a small latency cost; otherwise timings are omitted. Adds the SyncWord type (now exported at the package top level).

0.64.29 — sync/v1 package restructure

• Move the SyncTranscriber implementation into a versioned assemblyai.sync.v1 package to make room for future sync API versions. Public import paths are preserved — assemblyai.sync_api is now a thin re-export shim and top-level names (SyncTranscriber, SyncTranscriptionConfig, SyncTranscriptResponse, SyncTranscriptError, SyncWord) are unchanged.

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Generated by Copybara from internal master. Merging this PR publishes 0.64.29 to PyPI.