Add llm-prompt-default-max-tokens, open AI token limit fixes, parallel tool use fixes

What's Changed

• Fix breakage with Open AI's llm-chat-token-limit by @ahyatt in #77
• Fix Vertex and Open AI's parallel call tool use by @ahyatt in #78
• Add variable llm-prompt-default-max-tokens by @ahyatt in #79
• Fix how we look for ollama models in integration tests by @ahyatt in #80

Full Changelog: 0.17.3...0.17.4