Remote-execution client flow optimisation

Description

As described in #628 (closed)

Changes proposed:

• Added a message_digest function to utils.py to improve code reuse for this, might be better location for it.
• Checks action cache first, remotely executing if it didn't and then just pulling the result regardless. Done a bit of a refactor in the process.

This merge request, when approved, will close: #628 (closed)

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