fix: Supertonic 3 compatibility across all language examples

- README Quick Start: format `duration[0]` instead of the ndarray itself
  (numpy refuses `f"{ndarray:.2f}"`; matches official `dur[0]:.2f` pattern)
- py/example_pypi.py: print synthesized duration to mirror the docstring example
- Add `"na"` to AVAILABLE_LANGS / Languages.Available / availableLangs
  across all 11 runtimes (Python/Node/Web/Java/C++/C#/Go/Swift/Rust/Flutter/iOS)
  so the language-agnostic fallback advertised in the README actually passes
  per-runtime lang validation before being sent to the v3 ONNX duration predictor

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

go/helper.go

@@ -19,7 +19,7 @@ import (
 )
 
 // Available languages for multilingual TTS
-var AvailableLangs = []string{"en", "ko", "ja", "ar", "bg", "cs", "da", "de", "el", "es", "et", "fi", "fr", "hi", "hr", "hu", "id", "it", "lt", "lv", "nl", "pl", "pt", "ro", "ru", "sk", "sl", "sv", "tr", "uk", "vi"}
+var AvailableLangs = []string{"en", "ko", "ja", "ar", "bg", "cs", "da", "de", "el", "es", "et", "fi", "fr", "hi", "hr", "hu", "id", "it", "lt", "lv", "nl", "pl", "pt", "ro", "ru", "sk", "sl", "sv", "tr", "uk", "vi", "na"}
 
 // Config structures
 type SpecProcessorConfig struct {