Prompty does not work on old Python versions

[zzn2]

I found that prompty can be installed successfully on Python 3.9 but cannot be imported due to the following error:

Python 3.9.18 (main, Sep 11 2023, 13:41:44) 
[GCC 11.2.0] :: Anaconda, Inc. on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import prompty
Traceback (most recent call last):
  File "/home/zhizhu/miniconda3/envs/py39/lib/python3.9/site-packages/pydantic/_internal/_typing_extra.py", line 303, in _eval_type_backport
    return _eval_type(value, globalns, localns, type_params)
  File "/home/zhizhu/miniconda3/envs/py39/lib/python3.9/site-packages/pydantic/_internal/_typing_extra.py", line 332, in _eval_type
    return typing._eval_type(  # type: ignore
  File "/home/zhizhu/miniconda3/envs/py39/lib/python3.9/typing.py", line 292, in _eval_type
    return t._evaluate(globalns, localns, recursive_guard)
  File "/home/zhizhu/miniconda3/envs/py39/lib/python3.9/typing.py", line 554, in _evaluate
    eval(self.__forward_code__, globalns, localns),
  File "<string>", line 1, in <module>
TypeError: unsupported operand type(s) for |: 'type' and 'type'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/zhizhu/miniconda3/envs/py39/lib/python3.9/site-packages/prompty/__init__.py", line 7, in <module>
    from prompty.core import (
  File "/home/zhizhu/miniconda3/envs/py39/lib/python3.9/site-packages/prompty/core.py", line 20, in <module>
    class PropertySettings(BaseModel):
  File "/home/zhizhu/miniconda3/envs/py39/lib/python3.9/site-packages/pydantic/_internal/_model_construction.py", line 219, in __new__
    set_model_fields(cls, bases, config_wrapper, types_namespace)
  File "/home/zhizhu/miniconda3/envs/py39/lib/python3.9/site-packages/pydantic/_internal/_model_construction.py", line 512, in set_model_fields
    fields, class_vars = collect_model_fields(cls, bases, config_wrapper, types_namespace, typevars_map=typevars_map)
  File "/home/zhizhu/miniconda3/envs/py39/lib/python3.9/site-packages/pydantic/_internal/_fields.py", line 105, in collect_model_fields
    type_hints = get_cls_type_hints_lenient(cls, types_namespace)
  File "/home/zhizhu/miniconda3/envs/py39/lib/python3.9/site-packages/pydantic/_internal/_typing_extra.py", line 245, in get_cls_type_hints_lenient
    hints[name] = eval_type_lenient(value, globalns, localns)
  File "/home/zhizhu/miniconda3/envs/py39/lib/python3.9/site-packages/pydantic/_internal/_typing_extra.py", line 257, in eval_type_lenient
    return eval_type_backport(value, globalns, localns)
  File "/home/zhizhu/miniconda3/envs/py39/lib/python3.9/site-packages/pydantic/_internal/_typing_extra.py", line 279, in eval_type_backport
    return _eval_type_backport(value, globalns, localns, type_params)
  File "/home/zhizhu/miniconda3/envs/py39/lib/python3.9/site-packages/pydantic/_internal/_typing_extra.py", line 311, in _eval_type_backport
    raise TypeError(
TypeError: Unable to evaluate type annotation 'str | int | float | List | dict | bool'. If you are making use of the new typing syntax (unions using `|` since Python 3.10 or builtins subscripting since Python 3.9), you should either replace the use of new syntax with the existing `typing` constructs or install the `eval_type_backport` package.
>>>

It seems that the code is using a new type annotation style that older Python versions do not support.

Do we have plan adding compatible support for legacy Python versions like Python 3.8 or 3.9?