PERF: Preload `LetterAvatar.image_magick_version` in master process. (PR #12980)

It is wasteful to run the clean up and command to generate the version digest on every unicorn child process.


We can parallelize some of this stuff. No need to do all the warmup serially.

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end, do

@SamSaffron Updated :slight_smile: Using threads here shaved about 50ms off.

Request change