chore: split embedders in individual files

[smoya]

This PR refactors the existing projects/pgai/pgai/embeddings.py file by splitting it into smaller files, each containing a single class for a specific embedding provider (atm: voyageai, openai, ollama).

The primary goal is to improve maintainability and prevent the file from growing indefinitely over time, which can make it harder to manage and navigate.

[smoya]

Class is unmodified, except for this required imports.

[smoya]

Class is unmodified, except for this required imports.

[smoya]

Class is unmodified, except for this required imports.

[cevian]

LGTM but lets also have @JamesGuthrie review

[JamesGuthrie]

Do we need this __all__? According to this:

if a package’s __init__.py code defines a list named __all__, it is taken to be the list of module names that should be imported when from package import * is encountered

This seems like somewhat esoteric functionality, which we're not actively using, and I don't see the need to support. By removing it we can remove one more instruction in the readme above.

[smoya]

I made this in order to be able to import all providers through the same module: from .embedders import Ollama, OpenAI, VoyageAI The alternative (unless you know another one) would be to use individual imports such as:

from .embedders.ollama import Ollama
from .embedders.openai import OpenAI
from .embedders.voyageai import VoyageAI

I'm fine with this one and removing the content of the __init__.py. Removing that step which I agree it would be one less step to consider when adding a new provider.

EDIT: Another alternative in between would be just to remove the __all__ from but keep the imports in the __init__.py:

# __init__.py file
from .ollama import Ollama
from .openai import OpenAI
from .voyageai import VoyageAI

In that way we can still do the from .embedders import Ollama, OpenAI, VoyageAI (When I coded this, I believed the __all__ was necessary but it is not).

WDYT @JamesGuthrie ?

[JamesGuthrie]

Thanks for the explanation! I don't have a strong opinion, but the second suggestions (imports in __init__.py) is "less magical", so I would prefer it over __all__.

[smoya]

Awesome, thanks for the fast answer. Code (and docs) updated with the second option.

[smoya]

The redundant alias is needed, otherwise the linter will complain and provide the only alternative of adding it to the __all__ var