`qtype convert module` generates invalid type `PrimitiveTypeEnum.text` for optional parameters with defaults

[loukratz-bv]

Description:

When converting a Python module with optional parameters that have default values, qtype convert module generates invalid type references like PrimitiveTypeEnum.text? instead of text?.

Reproduction:

Create a simple Python module:

# example_tools.py
def my_function(required_param: str, optional_param: str = "default") -> str:
    """Example function with optional parameter."""
    return f"{required_param}-{optional_param}"

Convert it:

qtype convert module example_tools -o output.yaml

Expected Output:

- inputs:
  - id: required_param
    type: text
  - id: optional_param
    type: text?

Actual Output:

- inputs:
  - id: required_param
    type: text
  - id: optional_param
    type: PrimitiveTypeEnum.text?

Impact:

The generated YAML fails validation:

❌ Validation Error: Invalid type reference 'PrimitiveTypeEnum.text?'

Root Cause:

The type conversion logic is incorrectly serializing the enum type for optional parameters instead of using the string value.

Workaround:

Manually edit the generated YAML to replace PrimitiveTypeEnum.text? with text?.