FIX: Accept Iterable of Mappings from async step functions in functional API

[j-ittner]

This Pull Request introduces an enhancement to the Fluxus library's functional API, specifically targeting the step function and related classes within the conduit module. The changes expand the range of acceptable return types for functions passed to step, allowing for greater flexibility in asynchronous programming patterns.

Key Changes:

1. Expanded Awaitable Return Types:

   • The return type annotations for the step function and the Step class have been extended to include Awaitable[Iterable[Mapping[str, Any]]] and Awaitable[AsyncIterable[Mapping[str, Any]]]. This allows asynchronious functions passed to step to return not just single mappings/dictionaries but also iterables or async iterables of mappings/dictionaries.

2. Handling Awaitable Iterables:

   • Modifications in Step class implementation to properly handle and unwrap the new awaitable iterable return types. This ensures that the library can asynchronously process iterables of mappings/dictionaries.

Closes #24.

[AlexanderLontke]

Changes work as desired!