vcd2fsdb: no FIFO input, and .gz input is fully unpacked to temp files

Measured with the W-2024.09 converter. vcd2fsdb refuses a named pipe as input: rc 12 with 'is an empty file', also with -inc, and -h lists no stdin option. So you can't stream a VCD into it. A .gz input is not read in a stream either. The tool copies the .gz to /tmp/tmpXXXXXX.gz, then unpacks it to ./tmpXXXXXX in the current directory. Peak disk use is therefore gz + gz copy + full VCD + output, which is more than plain-VCD input. A killed run leaves both temp files behind, so clean them up in your guard. The FSDB output is not byte-deterministic: two runs on the same input give the same size but different bytes. Compare sizes and check content through a fsdb2vcd round trip, not by cmp. When sampling disk use, make the sampler interval much shorter than the job, otherwise short runs hide the temp unpack.