Refactor kokoro export (#2302)

- generate samples for https://k2-fsa.github.io/sherpa/onnx/tts/all/
- provide int8 model for kokoro v0.19 kokoro-int8-en-v0_19.tar.bz2

scripts/kokoro/v0.19/run.sh

@@ -0,0 +1,36 @@
+#!/usr/bin/env bash
+# Copyright    2025  Xiaomi Corp.        (authors: Fangjun Kuang)
+
+set -ex
+
+cat > README-new.md <<EOF
+# Introduction
+
+Files in this folder are from
+git clone https://huggingface.co/hexgrad/kLegacy
+EOF
+
+if [ ! -d kLegacy ]; then
+  git clone https://huggingface.co/hexgrad/kLegacy
+  pushd kLegacy/v0.19
+  git lfs pull
+  popd
+fi
+
+if [ ! -f ./voices.bin ]; then
+  ./generate_voices_bin.py
+fi
+
+if [ ! -f ./tokens.txt ]; then
+  ./generate_tokens.py
+fi
+
+if [ ! -f ./model.onnx ]; then
+  mv kLegacy/v0.19/kokoro-v0_19.onnx ./model.onnx
+fi
+
+./add_meta_data.py --model ./model.onnx
+
+if [ ! -f model.int8.onnx ]; then
+  ./dynamic_quantization.py
+fi