Include a functime.type_alias Module

[abstractqqq]

Typing is important. We all agree on that. Here we want to micmic Polars and have a functime specific type_alias module for the following purposes:

1. Custom typing for more complex and nested types. Right now I don't see any crazy types, but we might need this in the future.
2. Use Literal types for strategies in function calls instead of str. The advantage of using Literal["a", "b", "c", ..] is that a good linter can tell the user which are the available strategies, and can suggest the strategy based on what the user has typed in. On the other hand, a linter cannot infer anything from strings. (This is similar to Rust Enum, although more basic and only helps the linter, not the Python "compiler" or "interpreter".)
3. Have a centralized place to initialize constants, some parameters, custom types, instead of having all these stuff scattered around.