feat(mcp): preserve CallToolResult.isError flag in MCPToolResult#2118

Zelys-DFKH wants to merge 2 commits intostrands-agents:mainstrands-agents/sdk-python:mainfrom

Zelys-DFKH:fix/mcp-preserve-is-error-flagZelys-DFKH/sdk-python:fix/mcp-preserve-is-error-flagCopy head branch name to clipboard