Port BaseLoader + BaseTextSplitter interfaces and TextLoader + CharacterTextSplitter impl.

[realdavidvega]

This PR ports BaseLoader + BaseTextSplitter interfaces, and TextLoader + CharacterTextSplitter impl. respectively.

Also adds some simple tests.

[realdavidvega]

@franciscodr @nomisRev @gutiory @raulraja ready for review.

[nomisRev]

Awesome work @realdavidvega 🙌

I think we need to use nested use because both Source and Buffer are Closeable. That's what I did in PromptTemplate. Did you find anywhere in the docs, or code, that the Buffer wrapping the Source also closes the Source? If yes then the nested use is not needed, and can also be removed from PromptTemplate.

[realdavidvega]

Awesome work @realdavidvega 🙌

I think we need to use nested use because both Source and Buffer are Closeable. That's what I did in PromptTemplate. Did you find anywhere in the docs, or code, that the Buffer wrapping the Source also closes the
Source? If yes then the nested use is not needed, and can also be removed from PromptTemplate.

The documentation is a bit confusing, sometimes they use two nested use, but on other examples they are just using one FileSystem.source(path).buffer().use.

Also seems there's a documented function FileSystem.read() that is used to: "buffer the source before our block and close the source afterwards.", which does the same. So maybe we could use that function instead.