Move postprocess out of the predict lock

[squidarth]

Is your feature request related to a problem? Please describe.

Right now, the postprocess function in Truss is run within the context of the predict lock. This means that there is less concurrency available in postprocess than there ought to be.

Describe the solution you'd like

Move postprocess outside of predict lock.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
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