fix: ollama provider implementation

[jdurand]

fixes ollama api endpoint and request format to properly work with native ollama api

changes:

• refactored response parsing logic to skip empty/nil lines for all providers
• fixed ollama endpoint path to use native api format
• fixed request payload structure for ollama compatibility
• added proper message parsing for ollama responses
• removed unnecessary headers for ollama requests
• fixed cursor position validation to prevent 'Cursor position outside buffer' errors