Improve edge case validation for GeneralConfig.get_num_threads

[ashsong-nv]

There is a minor input validation bug for src/cve/data_models/config.py GeneralConfig.get_num_threads:

The field validator appears to expect invalid values:

    @field_validator("num_threads")
    @classmethod
    def get_num_threads(cls, v: int) -> int:
        if v is None or v < 1:
            return os.cpu_count() or 1

        return v

However this runs after Pydantic's own PositiveInt validator. So the validator effectively does nothing and GeneralConfig(num_threads=None) will raise a ValidationError. Setting @field_validator("num_threads", mode="before") fixes the issue.

The reason we need the field validator:

• os.cpu_count() sometimes returns None, the validator will supply a value of 1 in that situation
• The validator will replace values of None and anything <1 with os.cpu_count()