Output bindings not correctly supported when used with result processing triggers

### Description

When using the .NET Worker in Azure Functions, there is an issue with how the output binding model works when the function is triggered by a result-processing trigger. Specifically, there is ambiguity around where the function’s result should be assigned. As a result, the wrong result may be mapped to the trigger or the output bindings.

We need this scenario to be correctly supported. There should be a clear mechanism to indicate how the binding result is processed so that the output bindings receive the intended data and the trigger does not receive invalid results.

### Steps to reproduce

Use a result-processing trigger (e.g., McpToolTrigger) and a blob output binding.

Start by reproducing the issue with an McpToolTrigger and a blob output binding in the .NET Worker. Trace how the function result is assigned and processed for the trigger and output binding; done means the intended data reaches the blob output and the trigger does not receive an invalid result.

Written by the indexing model from the issue text.