Misc useful implementations

[DanielGMorenaFhecor]

@MestreCarlos has developed several methods needed to compute specific results. These functions could be valuable to include in the package, either as utility classes or as new methods in the current classes (this is still to be discussed).

The functions are as follows:

• def calculate_cracking_moment(section: GenericSection, n=0, plot=False) Description: Computes the cracking moment of a reinforced concrete (R.C.) section.
• def calculate_width_at_z(geometry: CompoundGeometry | GenericSection, z) Description: Calculates the width of a section or a section part at a certain level of z.
• def effective_depth(section: GenericSection, neg_bending: bool = False) Description: Determines the effective depth of a section, considering whether it is subject to negative bending or not.

For the implementation details, please refer to the corresponding file.