Emoji

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* Update to Unicode 16.0

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* `typing_extensions` dependency not required on Python 3.9 and higher 303

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* Read JSON files in binary mode to avoid UnicodeDecodeError 305

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* Use JSON files to store the database of emoji
* Load a language into emoji.EMOJI_DATA with emoji.config.load_language("zh")

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* `typing-extensions` requires at least version `4.7.0` 297

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* Move type annotations inline
* Use `functools.lru_cache` for looking up emoji by name with `get_emoji_by_name()`
* Move internal functions `get_emoji_unicode_dict()`, `get_aliases_unicode_dict()`, `_EMOJI_UNICODE` and `_ALIASES_UNICODE` to `testutils`
* Add type hints to tests
* Remove obsolete dev dependency `coveralls`