Add `inputs_from_state` and `outputs_to_state` support to `MCPToolset`

[sjrl]

Add support for inputs_from_state and outputs_to_state to MCPToolset. This is already supported for MCPTool, but is missing for MCPToolset.

As a follow up to @tstadel 's PR deepset-ai/haystack#10279 we should enable state-based configuration for MCPToolset. This would allow MCPTools to also take and add to State.

One thing to consider is that MCPToolset can contain multiple tools, so a single inputs_from_state and outputs_to_state configuration is not enough. Each tool in the toolset will need its own mapping.

One idea is to introduce per-tool state configuration, for example:

state_input_configs = {
    "tool_name_1": inputs_from_state_1,
    "tool_name_2": inputs_from_state_2,
}

A similar structure would be needed for outputs_to_state.

cc @vblagoje

P.S. This request originally came from Solution Engineers.