v3.5: Streaming, volume fixes, diagnostics

What's New

Features

• TTS Streaming – Reduced latency with streaming support (HA 2025.7+)
• Reconfigure flow – Change API key and URL without recreating the entity
• Sub-entries support – Multiple TTS agents under one integration (HA 2025.7+)
• Diagnostics – Added diagnostics support for troubleshooting
• Duration metadata – Reliable MP3 duration embedding using mutagen

Bug Fixes

• Fixed volume restoration timing for chime/normalize mode
• Fixed chime settings not applied from entity configuration
• Fixed voice/model changes not taking effect (cache key issue)
• Fixed ffmpeg metadata error (switched to mutagen library)
• Fixed "expected str" error on empty instructions field

Improvements

• Improved volume restoration logic and timing
• Complete translations (Czech, German, Greek, English)
• Code quality improvements and type annotations
• HACS and Hassfest validation workflows