PSCAD .inf load fails when duplicate headers exist across generated .out files #2
Description
Loading certain PSCAD .inf files now crashes in load_inf_file when the vendored PSCADVar tries to merge the .out chunks into a single DataFrame. If multiple .out files contain identical variable labels (e.g., Lgrid, Fgrid, Rgrid, Angle_Vg), pandas raises MergeError: Passing 'suffixes' which cause duplicate columns {...} is not allowed during the reduce(pd.merge(...)) step. Because we only rename columns by index/time positions, the duplicates collide after the first merge, preventing the combined CSV from being created. We need to detect or rename duplicate headers before merging (e.g., append file-specific suffixes) so PSCAD .inf files with repeated channel names successfully convert.