Remove unused pydantic_numpy import from spectrum.py

[Copilot]

pydantic_numpy was imported in spectrum.py but not declared as a dependency. The Frequency and LogFrequency classes using it are not referenced anywhere in the codebase.

Changes

• Removed pydantic_numpy.typing.Np1DArray import
• Changed field type from Np1DArray to list[float] (Pydantic-native)
• Updated Frequency properties to convert list to numpy array on access
• Removed numpy return type annotation from LogFrequency.__call__

# Before
from pydantic_numpy.typing import Np1DArray

class Frequency(RompyBaseModel):
    freq: Np1DArray = Field(description="Frequency array")
    
    @property
    def f0(self):
        return self.freq.min()

# After
class Frequency(RompyBaseModel):
    freq: list[float] = Field(description="Frequency array")
    
    @property
    def f0(self):
        return np.array(self.freq).min()

Original prompt

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This section details on the original issue you should resolve

<issue_title>Package pydantic_numpy missing in dependencies</issue_title>
<issue_description>pydantic-numpy isn't listed as a dependency in pyproject.toml but is imported in core/spectrum.py.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Package pydantic_numpy missing in dependencies #17

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