raw2trace is slow on large traces

Split from #1729 (closed)

On a 67GB bzip2 test raw trace, raw2trace ran for 53 mins and made a 156GB file before running out of disk space.

It took 1:09 to process a 1.1GB raw file and produce a 4GB trace.

We could cache the instr type info to avoid re-decoding on every bb execution.

If we do that, we should share it with the analysis tool opcode query impl if we end up adding such a thing.