chore: split into multiple files

[njbrake]

Description

A whole bunch of stuff was stuffed into the providers.py file. I'm prepping work for the #381 Public API PR, and to make that PR cleaner I figured I would do this first re-org here.

The file structure will change a bit more when I implement the Public API PR, but this handles the initial cleanup

PR Type

💅 Refactor ## Relevant issues

Checklist

• I have added unit tests that prove my fix/feature works
• New and existing tests pass locally
• Documentation was updated where necessary
• I have read and followed the contribution guidelines```

[codecov]

Codecov Report

❌ Patch coverage is 93.15068% with 10 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/any_llm/factory.py	85.71%	10 Missing ⚠️

Files with missing lines	Coverage Δ
src/any_llm/__init__.py	100.00% <100.00%> (ø)
src/any_llm/api.py	32.74% <100.00%> (+11.12%)	⬆️
src/any_llm/config.py	100.00% <100.00%> (ø)
src/any_llm/constants.py	100.00% <100.00%> (ø)
src/any_llm/provider.py	73.91% <100.00%> (+12.87%)	⬆️
src/any_llm/providers/bedrock/bedrock.py	61.11% <100.00%> (ø)
src/any_llm/providers/gemini/base.py	70.94% <100.00%> (ø)
src/any_llm/providers/gemini/gemini.py	100.00% <100.00%> (ø)
src/any_llm/providers/llamafile/llamafile.py	100.00% <100.00%> (ø)
src/any_llm/providers/lmstudio/lmstudio.py	100.00% <100.00%> (ø)
... and 6 more

... and 79 files with indirect coverage changes

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