Fix farfield rE dimensionalization - #936
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The radiation-zone field r E_inf written to farfield-rE.csv is a field times a distance, i.e. a voltage, but Measurement::Dimensionalize converted it with Nondimensionalize<FIELD_E> (and the reload path applied the same conversion again). The written values were rE / E_c instead of rE * V_c, off by the factor L_c / Z_0 and hence dependent on the internal characteristic length: for the dipole antenna example (L_c = 12 m) the reported far field was ~31x too small, while a run of the same model with L_c = 1 m gave values 12x larger with every other output unchanged. The radiated power integrated from the written far field was (L_c / Z_0)^2 of the accepted port power; with the correct voltage scale it agrees to 0.3 %. Normalized radiation patterns and the Stratton-Chu kernel (tested against the analytic dipole with the voltage scale) were unaffected. Use the VOLTAGE scale in both conversion directions. The idempotent PostOperator measurement test now carries far-field samples and checks that the conversion round-trips and that |rE| dimensionalizes as the probe field (V/m) times the length scale (m); both checks fail on the previous code.
Multiply the six r*E columns of the five farfield-rE.csv references by Z_0 / L_c, the exact factor of the unit fix in the previous commit (L_c = 12 m for the antenna cases, x31.394193; L_c = 4.5 mm for the CPW lumped cases, x83717.847), leaving all other columns byte-identical. Regenerating the files with the fixed code reproduces the transformed values to <= 6e-6 (MPI partition noise), and the five cases pass the regression suite against them.
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Fixes #935