Add Thai text preprocessing: number-to-text conversion and mai yamok expansion

[Copilot]

Implements preprocessing for Thai TTS to handle numbers and the repetition character (ๆ). Without preprocessing, TTS models synthesize digits literally ("1-2-3") and cannot interpret the Thai repetition marker.

Changes

• pythaitts/preprocess.py: New module with three functions

  • num_to_thai(): Converts numerals to Thai words (supports 0-9,999,999, decimals, negatives)
  • expand_maiyamok(): Expands ๆ by repeating the preceding word/syllable
  • preprocess_text(): Combines both transformations with selective disable options

• pythaitts/__init__.py:

  • Added preprocess parameter to TTS.tts() (enabled by default)
  • Exported preprocessing functions at package level

• Documentation: Updated README and Sphinx docs with usage examples

• Tests: 17 unit tests covering number conversion, mai yamok expansion, edge cases

Usage

from pythaitts import TTS, preprocess_text

# Automatic preprocessing
tts = TTS()
tts.tts("มี 5 คนๆ")  # Internally: "มี 5 คนๆ" → "มี ห้า คนคน"

# Direct preprocessing
preprocess_text("ฉันมี 123 บาท")  # → "ฉันมี หนึ่งร้อยยี่สิบสาม บาท"

# Disable if needed
tts.tts("มี 5 คนๆ", preprocess=False)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[TODO] Add preprocessing text for Thai text</issue_title>
<issue_description>[TODO] Add preprocessing text for Thai text

• Number to Thai text
• ๆ

...</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [TODO] Add preprocessing text for Thai text #1

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