SmolAgentsAdapter fails on tools with no input parameters (missing properties field)

[lordmathis]

The SmolAgentsAdapter.adapt() method crashes with a KeyError: 'properties' when processing MCP tools that have no input parameters.

Steps to Reproduce:

1. Connect to an MCP server that has at least one tool with no input parameters (e.g., a tool that just returns server version)
2. The tool's input schema will be valid JSON Schema: {"type": "object"}
3. Try to load the tools via smolagents MCPClient

Expected Behavior:

Tools with no input parameters should be supported. A JSON Schema of {"type": "object"} without properties is valid and indicates no parameters are required.

Actual Behavior:

The adapter crashes at line 103 in smolagents_adapter.py:
for k, v in input_schema["properties"].items():

This line assumes properties always exists, which is not true for parameter-less tools.

I'd be happy to provide a fix, if confirmed.