Update MockPipelineScriptCPS.groovy

[AbhinavJha1023]

Better Serialization: Uses transient for cachedVariables to prevent serialization issues.
Thread Safety: Uses Collections.synchronizedMap() to avoid concurrency issues.
Explicit Casting and Suppression: Handles type safety with @SuppressWarnings("unchecked").
Performance Optimization: Uses HashMap directly instead of relying on clone().

Testing done

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[nre-ableton]

First, thanks for your contribution and sorry for the delay on reviewing.

Aside from several style nitpicks (namely semicolons, empty lines, etc), I don't understand the point of this PR. Why bother writing to cachedVariables if it never gets read from?

This PR would also be easier to review if each of the changes mentioned in the commit message were a separate commit. That's a minor concern, though.