Allow rejected tool function to be async in order to ask user for a reason

[augustocdias]

One thing I find useful in Avante is when you reject an execution of a tool call to provide for a reason to the LLM, so it can decide to proceed, abort or even retry with different inputs. It would be nice to let the rejected function in the output to handle async in the same fashion as the actual tool so that we can call vim.ui.input to ask the user for a reason.

Another suggestion would be to add a flag for code_companion to handle this internally by itself.

[olimorris]

Awesome idea. I'll put that on my list

[olimorris]

This has been added in #2249

[augustocdias]

Thank you for the amazing work in this plugin :)