Parallelize the flash runner

[nolangormley]

The flash runner should be easy to split into parallel tasks since the algorithm is independent on a source/signal/geo split.

[nolangormley]

PR in #1

most of the way done, I need to get with Ananya and figure out the final bit

[nolangormley]

@Ananya-Joshi reviewed yesterday and pushed changes to fix the 'bring together step'. Going to benchmark today or Monday before moving on.

[nolangormley]

Ran on production through cronicle yesterday. Speedup is not as fast as we would have liked it, but it's acceptable for now. Ironing out a couple of bugs

[nolangormley]

Running with cronicle now. Going to keep an eye on it for a few days