Generate parameters when parsing prior distributions

[mhovd]

The CSV deserialization methods in both Theta::from_csv and Psi::from_csv create empty Parameters without preserving parameter metadata. This limitation should be documented in the function's docstring to inform users that they need to set parameters separately after loading from CSV.

    /// Each row represents a support point, each column represents a parameter.
    /// 
    /// Note: This only reads the matrix values and does not preserve or load parameter metadata.
    /// The returned `Theta` will have empty `Parameters`. You must set the parameters separately after loading from CSV.

Originally posted by @Copilot in #178 (comment)

[mhovd]

We also need to parse the probabilities, changing the return signature to a result which provides both Theta and an Option(Weights) .