Report waveform converter write cost as MB/s of source VCD, single-threaded CPU, so it lines up with published numbers

Published write-side numbers for waveform formats are almost always given as conversion throughput in MB of input VCD per second (the GTKWave FST manual's vcd2fst figures, and academic VCD compressors), plus compression ratio. To make a new converter comparable, report the same unit: VCD bytes divided by user+sys CPU seconds of the whole VCD-to-final-file path (all stages summed), measured serially on an idle machine. Also give the competitor measured on the same host today, because the old published figures are from much older CPUs and flatter a slow converter. Example arithmetic: 2.15 GB in 29.9 CPU-s is about 72 MB/s against about 125 MB/s for FST zlib + repack on the same box, which looks fine next to the old manual's numbers but is 1.7x behind in a same-host comparison.