add option to provide own buffer for output

[linusboehm]

I like using scratch buffers (from snacks.nvim) to execute small lua/python code snippets. I'd like to use it for C++ to get the assembly from godbolt. Currently the assembly is displayed in a new split behind the floating scratch buffer, which is hard to see. Therefore, it would be great if there was an option for the user to provide a buffer that is populated with the output.