Fix error in equality method for bearing elements

[jguarato]

Closes #1100

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An AttributeError occurs when running the analysis of a rotor with ball bearings due to an issue in the __eq__ method of the BearingElement class. This method checks for equality between elements but fails when comparing instances of the BallBearingElement class. The error arises because some arguments used during the initialization of a BallBearingElement instance (such as n_balls, d_balls, fs, and alpha) are not stored as attributes of the object, leading to a mismatch in the comparison.

To resolve this issue, the list of attributes to be compared in the __eq__ method was refined. The comparison now uses the intersection of the initialization arguments and the object's attribute names, ensuring that only relevant attributes are considered when checking for equality.

[jguarato]

I used this PR to fix an issue that arose when comparing bearing elements with attributes of different sizes (this error occurred when I tried to run the tutorial part 2).

Additionally, I noticed a similar error reported in issue #1100 was happening when attempting to save a rotor .toml file containing a BallBearingElement. As a result, some adjustments were made to the save() method of the BearingElement class.