由于我对你提到的一揽子计划有疑问（见我上面的评论），我建议你自己实施。
Pydantic文档解释了如何自定义设置源。为了确保嵌套字典“适当地”更新，您还可以使用非常方便的pydantic.utils.deep_update函数。
显然，您需要安装pyyaml才能使其工作。
下面是一个例子：

from pathlib import Path
from typing import Any

from pydantic import BaseSettings as PydanticBaseSettings
from pydantic.env_settings import SettingsSourceCallable
from pydantic.utils import deep_update
from yaml import safe_load

THIS_DIR = Path(__file__).parent

class BaseSettings(PydanticBaseSettings):
    test_api_one: dict[str, str]

    class Config:
        config_files = [
            Path(THIS_DIR, "global.yaml"),
            Path(THIS_DIR, "dev.yaml"),
        ]

        @classmethod
        def customise_sources(
                cls,
                init_settings: SettingsSourceCallable,
                env_settings: SettingsSourceCallable,
                file_secret_settings: SettingsSourceCallable
        ) -> tuple[SettingsSourceCallable, ...]:
            return init_settings, env_settings, config_file_settings

def config_file_settings(settings: PydanticBaseSettings) -> dict[str, Any]:
    config: dict[str, Any] = {}
    if not isinstance(settings, BaseSettings):
        return config
    for path in settings.Config.config_files:
        if not path.is_file():
            print(f"No file found at `{path.resolve()}`")
            continue
        print(f"Reading config file `{path.resolve()}`")
        if path.suffix in {".yaml", ".yml"}:
            config = deep_update(config, load_yaml(path))
        else:
            print(f"Unknown config file extension `{path.suffix}`")
    return config

def load_yaml(path: Path) -> dict[str, Any]:
    with Path(path).open("r") as f:
        config = safe_load(f)
    if not isinstance(config, dict):
        raise TypeError(
            f"Config file has no top-level mapping: {path}"
        )
    return config

现在假设这些是有问题的文件：
global.yaml

test_api_one:
  date_format: '%Y-%m-%d'
  date_time_format: '%Y-%m-%dT%H:%M:%SZ'

dev.yaml

test_api_one:
  uri: 'https://dev_api/'
  secret: dev

执行print(BaseSettings().json(indent=4))的输出是这样的：
一个三个三个一个