Fix bugs and add Gemini API compatibility

[realshovanshah]

Summary

This PR fixes three bugs in Neural and adds compatibility with OpenAI-compatible APIs that don't support penalty parameters (e.g., Google Gemini).

Changes

1. Fix undefined variable in s:LoadProvider()

File: autoload/neural.vim:250

User configuration was not being passed to the provider script due to using config instead of l:config.

- let l:provider.config = config
+ let l:provider.config = l:config

2. Fix frequency_penalty typo

File: src/neural/provider/openai.py:209

frequency_penalty was being set to presence_penalty value instead of its own value.

- frequency_penalty=presence_penalty,
+ frequency_penalty=frequency_penalty,

3. Make penalty parameters optional

File: src/neural/provider/openai.py:60-68

Some OpenAI-compatible APIs (like Gemini) don't support penalty parameters and return 400 errors even when they're set to 0. This change only includes penalty parameters in the request when they're non-zero.

Testing

• Verified all three fixes resolve the issues
• Tested with Gemini API: works with penalties=0 (excluded from request)
• Tested backward compatibility: OpenAI still works with non-zero penalties

Gemini Configuration Example

let g:neural = {
\   'providers': [
\       {
\           'type': 'openai',
\           'url': 'https://generativelanguage.googleapis.com/v1beta/openai',
\           'api_key': $GEMINI_API_KEY,
\           'model': 'gemini-2.5-flash',
\           'use_chat_api': v:true,
\           'presence_penalty': 0,
\           'frequency_penalty': 0,
\       },
\   ],
\}

[w0rp]

I appreciate the effort here and I encourage you to maintain your own fork. @Angelchev and I have recently started work on a complete rewrite of Neural probably absolutely loaded with breaking changes that'll be much better.

I'll be replaying all of the commits for the brand new version on top of this repository and see what we can do to make the existing commands work or not in the new plugins.

We're planning on shipping two separate plugins for Vim and Neovim that use Vim9script and Lua respectively, with a FOSS compiled Zig middleware. Can't say when it will be ready, but hopefully later this year.

[w0rp]

Having shared the above, if/when you mark this ready for review I will merge it.

[realshovanshah]

oh - looks like you're right, this diff got Gemini working for me but looks like supporting all the features is a different beast altogether.

looking forward to the rewrite then!! i don't see a lot of LLM-related plugins for good old Vim for some reason.

please feel free to close the PR. (and btw, why not mention the coming update in the readme?)

[w0rp]

why not mention the coming update in the readme?

We will tell everyone soon enough! We've been rapidly developing a new version where the shape of it keeps changing.