chore: Introduce FileHandler

[sdn4z]

First MR towards having cache file, that will save the trusted packages in the local file system (#143).

Created a new class FileHandler, which will hold all the interactions towards reading/writing files.

Adapted AbstractParser to use it.

In the following MRs:

• adapt ConfigHandler to also use it.
• save trusted packages to a file.

[scastlara]

Looks reasonable! Can you give me 2cents on what you mean by caching the file? I assume you mean vendoring it in the repository?

[scastlara]

Suggested change

	def __init__(self, file_path: str, file_handler: BaseFileHandler = FileHandlerPathlib) -> None:
	def __init__(self, file_path: str, file_handler: type[BaseFileHandler] = FileHandlerPathlib) -> None:

[sdn4z]

Nice catch!

I was in doubt about receiving the FileHandler object directly or just the type though. For now I think it's fine, as long as we don't have another FileHandler type that requires some other parameters to initialize

[scastlara]

Usually, I'd say it's best to pass instances instead of classes. Unless you have a very good reason to defer the class instantiation.

[sdn4z]

After checking, I think it's best to just not make AbstractParser receive any FileHandler and assume it's going to use FileHandlerPathlib.

If we wanted to make it receive an object, DependencySelector should tell the AbstractParser which FileHandler to use, but right now I think it's safe to say that we only want one way of opening/reading files. I'd leave it like this, tying AbstractParser to FileHandlerPathlib, and see how it evolves if we agree :)

[sdn4z]

Looks reasonable! Can you give me 2cents on what you mean by caching the file? I assume you mean vendoring it in the repository?

That was the original idea but in a way, vendoring it in the repo would be just another source. So twyn would be mirroring the actual TopPypiReferences to guarantee more availability, and then we can provide different options to chose from where to retrieve the data.

The caching I'm referring to in this MR is a local one, so that you would save locally the list of trusted packages without having to download the whole list again.