[REFACTOR] Move `functions` module in Python SDK to a sub package

[georgeh0]

Currently functions.py is a single module with all functions. We want to convert it a sub package.

Similar to #1028 (which was for targets).

We want to have the following submodules for now:

• sbert: for SentenceTransformerEmbed function
• colpali: for Colpali related functions / utils
• _engine_builtin_specs: for everything else that with only spec class there (their real implementation is on Rust side)

Please make sure everything these sub modules are imported from __init__.py - so existing user code won't be broken.

[Davda-James]

will do it