Code execution tool improvements and web search/fetch response filtering

Code execution tool: Now supports code_execution_20260521, which discloses the 90-second per-cell execution time limit in the tool description so Claude can budget long-running cells. No beta header required.

Web search and fetch tools: Now support web_search_20260318 and web_fetch_20260318, adding a response_inclusion parameter to drop consumed result blocks from the API response for agentic workflows. No beta header required.