This PR removes the cppjieba dependency from the sherpa-onnx project by replacing its usage with character-based text processing. The main purpose is to simplify the codebase by eliminating the need for external jieba dictionary files and the cppjieba library.
- Replaces jieba-based word segmentation with UTF-8 character-level tokenization
- Removes all references to dict_dir and dictDir parameters across APIs
- Adds a new CharacterLexicon class to replace JiebaLexicon