Fixed "Custom field not found" error

[bmen25124]

Fixes: #117

I added unit tests to make sure it is working.

[ShineQi]

This fix will produce another error

 |   File "D:\open-webui\mcpo\src\mcpo\utils\main.py", line 183, in _process_schema_property
      |     item_type_hint, _ = _process_schema_property(
      |                         ^^^^^^^^^^^^^^^^^^^^^^^^^
      |   File "D:\open-webui\mcpo\src\mcpo\utils\main.py", line 156, in _process_schema_property
      |     nested_type_hint, nested_pydantic_field = _process_schema_property(
      |                                               ^^^^^^^^^^^^^^^^^^^^^^^^^
      |   File "D:\open-webui\mcpo\src\mcpo\utils\main.py", line 101, in _process_schema_property
      |     pydantic_field = Field(default=default_value, description=prop_desc)
      |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      |   File "D:\open-webui\mcpo\.venv\Lib\site-packages\pydantic\fields.py", line 1102, in Field
      |     return FieldInfo.from_field(
      |            ^^^^^^^^^^^^^^^^^^^^^
      |   File "D:\open-webui\mcpo\.venv\Lib\site-packages\pydantic\fields.py", line 288, in from_field
      |     return FieldInfo(default=default, **kwargs)
      |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      |   File "D:\open-webui\mcpo\.venv\Lib\site-packages\pydantic\fields.py", line 234, in __init__
      |     alias_is_set = any(alias is not None for alias in (self.alias, self.validation_alias, self.serialization_alias))
      |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      | RecursionError: maximum recursion depth exceeded

with

{
  "mcpServers": {
    "mcp-server-chart": {
      "command": "npx",
      "args": [
        "-y",
        "@antv/mcp-server-chart"
      ],
      "name": "mcp-server-chart"
    }
}

[bmen25124]

Unfortunately, I'm not available for the fix, I'll not be here for a while. Feel free to fix or create a new PR for the issue.

[bipedalBit]

This fix will produce another error

 |   File "D:\open-webui\mcpo\src\mcpo\utils\main.py", line 183, in _process_schema_property
      |     item_type_hint, _ = _process_schema_property(
      |                         ^^^^^^^^^^^^^^^^^^^^^^^^^
      |   File "D:\open-webui\mcpo\src\mcpo\utils\main.py", line 156, in _process_schema_property
      |     nested_type_hint, nested_pydantic_field = _process_schema_property(
      |                                               ^^^^^^^^^^^^^^^^^^^^^^^^^
      |   File "D:\open-webui\mcpo\src\mcpo\utils\main.py", line 101, in _process_schema_property
      |     pydantic_field = Field(default=default_value, description=prop_desc)
      |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      |   File "D:\open-webui\mcpo\.venv\Lib\site-packages\pydantic\fields.py", line 1102, in Field
      |     return FieldInfo.from_field(
      |            ^^^^^^^^^^^^^^^^^^^^^
      |   File "D:\open-webui\mcpo\.venv\Lib\site-packages\pydantic\fields.py", line 288, in from_field
      |     return FieldInfo(default=default, **kwargs)
      |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      |   File "D:\open-webui\mcpo\.venv\Lib\site-packages\pydantic\fields.py", line 234, in __init__
      |     alias_is_set = any(alias is not None for alias in (self.alias, self.validation_alias, self.serialization_alias))
      |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      | RecursionError: maximum recursion depth exceeded

with

{
  "mcpServers": {
    "mcp-server-chart": {
      "command": "npx",
      "args": [
        "-y",
        "@antv/mcp-server-chart"
      ],
      "name": "mcp-server-chart"
    }
}

Actually, the failure to start mcp-server-chart with mcpo and the "Custom field not found" error occur due to a $ref loop in the schema of mcp-server-chart's tool. To resolve this issue, you need to return the tuple (<python_type_hint>, <pydantic_field>)) at the appropriate time in the _process_schema_property() function within mcpo/utils/main.py to break this loop. I'm attempting to draft a commit for this fix.

A schema with a $ref causing loop for example:

{
    "type": "object",
    "properties": {
        "data": {
            "type": "object",
            "properties": {
                "name": {
                    "type": "string"
                },
                "children": {
                    "type": "array",
                    "items": {
                        "type": "object",
                        "properties": {
                            "name": {
                                "type": "string"
                            },
                            "children": {
                                "type": "array",
                                "items": {
                                    "$ref": "#/properties/data/properties/children/items"
                                }
                            }
                        },
                        "required": [
                            "name"
                        ]
                    }
                }
            },
            "required": [
                "name"
            ],
            "description": "Data for fishbone diagram chart, such as, { name: 'main topic', children: [{ name: 'topic 1', children: [{ name: 'subtopic 1-1' }] }."
        },
        "theme": {
            "type": "string",
            "enum": [
                "default",
                "academy"
            ],
            "default": "default",
            "description": "Set the theme for the chart, optional, default is 'default'."
        },
        "width": {
            "type": "number",
            "default": 600,
            "description": "Set the width of chart, default is 600."
        },
        "height": {
            "type": "number",
            "default": 400,
            "description": "Set the height of chart, default is 400."
        }
    },
    "required": [
        "data"
    ],
    "$schema": "http://json-schema.org/draft-07/schema#"
}

pr commited: #174