[Custom Issue]: Differencing two sets of output.

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### Contact Details

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### Are there any linked Issues or Pull Requests?

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### Brief description

It'd be useful to support a command-line tool which takes two sets of Vernier output and orders the profiled regions according to differences in timings. e.g. `vernier-diff /path/to/runA /path/to/runB`. If particular regions took longer in runB, then their timings would be -ve and appear at the top of the list.

```
Baseline file: baseline-file.out, procs: 0001, threads: 01
Test file: test-file.out, procs: 0001, threads: 01

Rank Routine name Time difference (s)
------- ------------------------------------------------------- -------------------
1 some_subroutine -20.565
2 another_subroutine -16.593
3 my_function -11.353
4 another_function 2.450
```

### Further details of the issue.

_No response_

No files, tests, or existing entry points are named. Start by locating Vernier's command-line interface and the code that reads profiler output, then determine how two runs can be matched and ranked by timing differences; done means a vernier-diff command produces the illustrated ordered report.

Written by the indexing model from the issue text.