Ability to use failures_first across Julia sessions #224

Follow-up to #172 / #212

So that we can re-start the repl, or even download an artifact from CI testing, and run tests starting with those failures.

I'm thinking failures_first="path/to/file" (implying failures_first=true) that loads the cache of tests statuses from that file (which could be empty) and which then writes to that file with the new statuses at the end of a run.

This file would need to be in some simple standard quick to read/write format, and contain a mapping of id => status e.g.

0x93817067fde4f95c,0
0xe6018cbc37d41b8b,1

or whatever

i think it's fine for this format to be documented not stable across ReTestItems minor versions (or Julia versions)

But it absolutely should be stable from CI -> local and vice versa