Add standard content mass properties retrieval

[csamid]

Summary

Adds standard_cont_mass_properties method to the Client class, enabling mass properties retrieval for standard content.

Testing

Testing was done using this onshape document After the changes the inertial tag for sub-asm-std-cont matches with the display mass properties window within onshape.

Inertial tag:

<inertial>
<origin xyz="3.9625718201122967351e-10 7.420351968363106984e-05 0.099769642737675509614" rpy="0 0 0"/>
<mass value="0.77420617546130443554" />
<inertia ixx="0.0026100719639290674741" ixy="-4.500337705738727131e-12"  ixz="1.3282237023637959534e-11" iyy="0.0026078954199623763377" iyz="3.4736360265661929318e-06" izz="6.2401832920398126923e-05" />
</inertial>

Output from display mass properties

Closes: #102

[Gregwar]

Thanks for contributing