Proposal - introduce call in ProvidedInstance

[Minitour]

Currently the ProvidedInstance offers a get_value function which returns the attribute based on the _attrs path. However if the returned attribute is a callable (aka function) then one needs to perform a "double call".

For example

session = providers.Singleton(Session)

 awsauth = providers.Singleton(
        AWS4Auth,
        session.provided.get_credentials.get_value()().access_key,
        session.provided.get_credentials.get_value()().secret_key,
        config.region(),
        'aoss',
        session_token=session.provided.get_credentials.get_value()().token
    )

Notice how we first get the value

# This returns the attribute `get_credentials` which is in fact a function
session.provided.get_credentials.get_value()

Then we need to invoke it to obtain the access_key

session.provided.get_credentials.get_value()().access_key,
#                                         ^^^^ - Not very elegant 

Proposal - Introduce a call function

class ProvidedInstance:
    def __init__(self, provided: "BaseProvider[Any]") -> None:
        self._provided = provided
        self._attrs: List[str] = []

    def __getattr__(self, attr: str) -> "ProvidedInstance":
        self._attrs.append(attr)
        return self

   def call() -> Any:
       func = self.get_value()
       return func()

    def get_value(self) -> Any:
        resolved_provider_object = self._provided()

        if not self._attrs:
            msg = (
                "Please provide at least one attribute. For example: provide.some_attr"
            )
            raise Exception(msg)

        attribute_path = ".".join(self._attrs)
        attr_value = _get_value_from_object_by_dotted_path(
            resolved_provider_object,
            attribute_path,
        )
        return attr_value

This would make the above example appear as:

session = providers.Singleton(Session)

 awsauth = providers.Singleton(
        AWS4Auth,
        session.provided.get_credentials.call().access_key,
        session.provided.get_credentials.call().secret_key,
        config.region(),
        'aoss',
        session_token=session.provided.get_credentials.call().token
    )