fix: include tool parameters and emit tool definitions on chat spans

- toolCallingLoop emits tool definitions with parameters (tool inputSchema) on the agent span and tools_available event, per OTel GenAI semantic conventions (fixes #300318).

- chatMLFetcher and BYOK providers (anthropic, gemini) now also set gen_ai.tool.definitions on each chat {model} child span so trace viewers can render the tool catalog per LLM call (fixes #299934).

- toToolDefinitions normalizer extended to handle OpenAI Responses API, Anthropic input_schema, and VS Code inputSchema shapes.