Support parsing anyOf from MCP tools

[duguyue100]

Smolagents uses MCPAdapt, one problem is that it doesn't handle anyOf field from the input schema.

To mitigate this problem, I expanded get_tool_json_schema function that parses the argument properly.

Here is an example of before and after the change:
Before:

    'lifecycle_stage': {'anyOf': [{'enum': ['development',
        'ideation',
        'r_and_d',
        'testing',
        'production',
        'retired'],
       'type': 'string'},
      {'type': 'null'}],
     'default': None,
     'description': 'The lifecycle stage of the Software.',
     'title': 'Lifecycle Stage',
     'type': 'string'},

After

    'lifecycle_stage': {'default': None,
     'description': 'The lifecycle stage of the Software',
     'title': 'Lifecycle Stage',
     'type': 'string',
     'nullable': True,
     'enum': ['development',
      'ideation',
      'r_and_d',
      'testing',
      'production',
      'retired']},

[aymeric-roucher]

Why this .pop?

[duguyue100]

If we parse anyOf, keeping it then results duplicated information. That's why we just pop the key after parsing it.

[aymeric-roucher]

We have a type "any", why not use it?

[duguyue100]

Please check line 247, this is how we parse Any all along, i'm just following the current practice here.

[aymeric-roucher]

We have type "null", why not use it?

[duguyue100]

This is covered by the nullable part above