Create a paper trail for delay models regarding how they were produced and can be reproduced

We should embed the following information into the delay model proto:
* commit hash, and whether the repo has any modified files
* paths source files used,
* any options

First, this information could be embedded in the data points proto generated by the `run_timing_characterization` script. Then, this info should be copied into the final delay model proto when the data points proto is combined with the op models proto.